Heterophilic antibody interference in immunometric assays

Multiplex analysis of ovarian cancer patients using glycan microarray

Investigation of tumor-associated glycan antigens (TAGs) could be helpful for the development of sensitive cancer diagnostics and novel therapies. Glycan microarrays are effective methods for analyzing glycans and anti-glycan antibodies, which are immobilized arrays of oligo- or poly-saccharides on different substrates, making them a promising class of oncological biomarkers. Blood serum samples from patients (n = 203) with ovarian cancer (OvaCan) and healthy volunteers were analyzed using a glycan microarray containing 63 immobilized glycans to determine changes in anti-glycan IgG and IgM antibody profiles in OvaCan. Levels of anti-glycan IgG and IgM antibodies in OvaCan statistically differed from levels in healthy donors: the most prominent statistically significant difference for anti-glycan IgG antibodies was found for 6-O-su-Lec (AUC = 0.657, Se = 48.0 %, and Sp = 73.3 %). The AUC values for certain glycans investigated in diagnosing OvaCan indicated a fingerprint consisting of IgM antibodies to specific glycans, and the most specific anti-glycan IgM antibodies were Ley (AUC = 0.625, Se = 98.0 % and Sp = 45.0 %). The potential of these serological biomarkers to distinguish between OvaCan and other malignancies is still an unresolved issue that requires more large-scale studies to confirm and validate the use of these biomarkers in the diagnosis of different types of cancer.

Adrenocorticotropic Hormone Measured by Immulite 1000 and Elecsys Assay Platforms in Suspected Cases of Hypocortisolism: A Word of Caution

OBJECTIVE

Several reports suggested that adrenocorticotropic hormone (ACTH) level measured by Immulite 1000 may be falsely elevated leading to misdiagnosis of etiology of Cushing syndrome. However, when it comes to fallacies of ACTH measurement in suspected cases of hypocortisolism, evidence is limited. We explored the performance of ACTH assays using Immulite 1000 and Elecsys Cobas immunoassay platforms in subjects with hypocortisolism.

METHODS

In this observational, cross-sectional study, 104 patients with haemoglobin E/beta-thalassemia were subjected to 9 am serum cortisol, direct renin concentration, and plasma aldosterone. Plasma ACTH was measured in Immulite 1000 and Elecsys Cobas platforms. Both 1 μg and 250 μg Synacthen stimulation tests were performed to diagnose adrenal insufficiency.

RESULTS

Among 104 patients with haemoglobin E/beta-thalassemia, 34 had primary adrenal insufficiency, 9 had secondary adrenal insufficiency, and 33 had subclinical adrenal insufficiency. Mean plasma ACTH (n = 104) measured by Immulite 1000 and Elecsys was 83.42 ± 63.46 pg/mL versus 52.10 ± 38.14 pg/mL, respectively (P < .001). The values had good correlation (r = 0.341, P < .001); however, the agreement between measured values was not strong (Cohen's κ = 0.208, P = .001). With regard to the diagnosis of primary adrenal insufficiency, specificity of Immulite 1000 was low compared with Elecsys (27.86% vs 80.32%). Furthermore, 2 patients with secondary adrenal insufficiency had inappropriately elevated ACTH measured at Immulite 1000 assay platform.

CONCLUSION

Use of Immulite 1000 platform may result in falsely elevated ACTH values. Physicians should exercise caution while interpreting the results and repeat test using a different assay platform may be considered.

Standard E TB-Feron ELISA and Standard F TB-Feron FIA positivity rates and agreement with QuantiFERON-TB Gold Plus among TB high-risk population in Bandung, Indonesia

Tuberculosis (TB) remains a global public health problem. The determination of tuberculosis infection (TBI) using interferon-gamma release assay has now been used widely. We aim to evaluate the positivity rates of Standard E TB-Feron enzyme-linked immunosorbent assay (TB-Feron ELISA) and Standard F TB-Feron fluorescent immunoassay (TB-Feron FIA) and their agreement with QuantiFERON-TB Gold Plus (QFT-Plus) among TB high-risk populations in Bandung City, Indonesia. We conducted a cross-sectional study, including people with a high risk of acquiring TB. We screened subjects for TB symptoms and offered chest X-ray (CXR). Anyone with cough or CXR suggestive of TB was asked to give sputum samples for GeneXpert MTB/RIF Ultra test. The positivity rates and corresponding 95% confidence intervals (CI) were calculated among patients with bacteriologically confirmed TB and among patients with no evidence of TB, no history of TB, and no known contact with TB patient (low risk of TBI). The agreement with QFT-Plus was calculated using Cohen's κ score. We enrolled 527 subjects, and the proportion of positive results among bacteriologically confirmed TB patients were 8 (53.3%; 95% CI 26.6-78.7), 9 (60.0%, 95% CI 32.3-83.7), and 10 (66.7%, 95% CI 38.4-88.8) by TB-Feron FIA, TB-Feron ELISA and QFT-Plus. The agreement between TB-Feron FIA and QFT-Plus among all subjects was similar to that of TB-Feron ELISA and QFT-Plus (84.1%, κ = 0.66, 95% CI 0.59-0.72). TB-Feron FIA and TB-Feron ELISA showed an acceptable clinical performance compared with QFT-Plus. These tests are useful alternatives for detecting TB infection.IMPORTANCEThis study evaluates the performance of two alternative interferon-gamma release assays, Standard E TB-Feron enzyme-linked immunosorbent assay and Standard F TB-Feron fluorescent immunoassay, for diagnosing tuberculosis infection (TBI) among high-risk populations in Bandung, Indonesia. Both assays demonstrated comparable clinical performance to the widely used QuantiFERON-TB Gold Plus (QFT-Plus). Given the global burden of tuberculosis, particularly in resource-limited settings, these findings suggest that the TB-Feron assays could serve as reliable alternatives to QFT-Plus for TBI detection. This research highlights the potential for these assays to improve tuberculosis diagnosis, offering a more accessible and efficient screening tool, especially for high-risk populations, and supporting broader tuberculosis surveillance.

PEG Precipitation to Detect Macro-TSH in Clinical Practice: A Systematic Review

Macro-thyroid-stimulating hormone (macro-TSH) is a complex formed by monomeric TSH with anti-TSH antibodies, causing falsely elevated TSH levels and potential misdiagnosis of hypothyroidism. Identification of macro-TSH is essential for proper treatment and patient follow-up. Its diagnostic gold standard is gel filtration chromatography (GFC), which is very expensive, time-consuming, and rarely available. Polyethylene glycol (PEG) precipitation is more accessible and inexpensive. The aim of the study was to review evidence on PEG precipitation for the detection of macro-TSH to standardize its application in clinical practice.

METHODS

According to PRISMA guidelines, we conducted up to August 2024 a comprehensive search of PubMed and Scopus databases, using terms related to macro-TSH and PEG precipitation.

RESULTS

We included 23 studies with 4476 subjects, encompassing 10 observational studies and 13 case series/reports. All studies showed a low risk of bias. They were conducted in tertiary centres and included newborns to elderly subjects. The most of evidence about the procedure has been achieved with PEG concentrations of 12.5%. The PEG-precipitable TSH of the macro-TSH cases was always higher than 75% ranging on average from 81% to 90%. No-macro-TSH cases (controls) showed a PEG-precipitable TSH percentage ranging from 44.1% to 61.8%.

CONCLUSIONS

PEG precipitation can be taken into account as a useful diagnostic tool for macro-TSH. However, it is necessary to perform PEG precipitation in cases with a highly suspicious clinical picture and at the same time perform all available ancillary tests. PEG-precipitable TSH > 75% can be considered a reliable diagnostic threshold for macro-TSH cases.

Review of Literature and Recommended Procedures for Management of Unusual Cases of False Positive Troponin Tests

Heterophile antibodies are immunoglobulins produced by the immune system in response to exposure to animal and bacterial antigens, blood transfusions, autoimmune disorders, hematologic malignancies, dialysis, and pregnancy. Recently, these antibodies have garnered significant attention due to their impact on the accuracy of laboratory test results. Heterophile antibodies can bind not only to specific antigens but also to those from different species, including the antibodies used in laboratory tests. This cross-reactivity with foreign proteins is the basis for their interference in immunological assays, such as those measuring cardiospecific troponins (cTn). This manuscript reviews the literature on cases of heterophile antibody interference in troponin testing and proposes an algorithm for identifying such interference when clinical discrepancies arise. Recognizing and addressing heterophile antibody interference is crucial, particularly for tests like those for troponins, which are key biomarkers in the diagnosis and management of emergency and intensive care patients. The literature emphasizes the need for accurate procedures to distinguish true cardiac damage from false positives, thereby preventing unnecessary additional tests and hospitalizations.

Troponin Test, Not Only a Number: An Unusual Case of False Positive

Heterophile antibodies, which can arise from infections, autoimmune disorders, or exposure to animal antigens, can interfere with immunoassays. These antibodies can cross-react with the test reagents used in troponin assays, causing a false elevation in troponin levels. The paper describes a case of a 37-year-old male drug abuser admitted to the emergency room with chest pain. A series of troponin measurements performed using different assays gave discrepant results. Only thanks to the use of Scantibodies HBT tubes, which remove heterophile antibodies, was it possible to make a correct diagnosis of troponin negativity. In conclusion, a correct laboratory/clinical approach to the identification of heterophile antibody interference is essential for accurate troponin testing in order to avoid false positive results. Implementing neutralizing tests can significantly improve the reliability of these diagnostic assays, ensuring better patient outcome.

PTH immunoassay interference: differential diagnosis with normocalcemic primary hyperparathyroidism?

The main diagnostic dilemma in normocalcemic hyperparathyroidism is differentiating this condition from secondary hyperparathyroidism and other causes of elevated parathyroid hormone (PTH) levels in eucalcemic patients, including potential assay interferences. Despite the analytical sensitivity of immunoassays, they may lack adequate accuracy due to several analytical interferences, such as the presence of heterophilic antibodies. Immunoassays for PTH measurement use the immunometric "sandwich" technique, and only a few cases of interference with this assay have been reported to date. We describe herein two patients in whom PTH immunoassay interference was demonstrated. Both patients presented high serum PTH levels, measured using a second-generation Roche electrochemiluminescence assay (ECLIA; Elecsys Roche, Germany), and normocalcemia. When immunoassay interference was suspected, PTH measurements were repeated using a different analytical platform, the 1-84 PTH third-generation Roche Elecsys ECLIA, resulting in normal levels. We subsequently performed serial dilutions using normal mouse serum with the second-generation ECLIA and found no linearity, indicating the presence of interference in both patients. Immunoassay interference may lead to misinterpretation of a patient's results by the laboratory and incorrect treatment planning by the attending physician. Despite its rarity, the presence of interferences in the PTH immunoassay resulting in falsely high PTH levels should be considered when the laboratory result does not match the patient's clinical presentation, thus preventing erroneous diagnoses and unnecessary therapeutic procedures.

[Combination of macro-TSH and macroprolactinemia phenomena in a patient with autoimmune thyroiditis and vitiligo]

Laboratory diagnostic methods are the main tools in the practice of a doctor of any specialty, including an endocrinologist. Factors were identified that could change the concentration of the biologically active fraction of the test substance, subsequently complicating the interpretation of laboratory results and making the right clinical decision. The literature describes a variety of circulating autoantibodies involved in binding to pituitary hormones (prolactin (PRL), thyroid-stimulating hormone (TSH), growth hormone, luteinizing, follicle-stimulating, and adrenocorticotropic hormones), hypothalamus (vasopressin and oxytocin), pancreas (insulin and glucagon) , parathyroid glands (parathyroid hormone), as well as with thyroid hormones. As a rule, the resulting macromolecules lead to an increase in laboratory parameters, in which the prevailing fraction of the hormone does not have biological activity, which determines the main problem of this phenomenon. The most common variants include immune complexes with PRL and TSH, causing the phenomena of macroprolactinemia and macrothyrotropinemia (macro-TSH-emia/macro-TSH), respectively. Most laboratory test systems used in clinical practice are capable of determining only the total amount of PRL and TSH. The presented clinical observation describes a combination of the phenomena of macro-TSH and macroprolactinemia in a patient with autoimmune thyroiditis (AIT) and vitiligo.

D-dimer assay interference detected by the discrepancy in D-dimer concentrations at different dilutions: a case report

This case report describes interference from heterophilic antibodies in D-dimer assay. The interference was suspected due to discrepancies between D-dimer concentrations in the original sample and diluted samples, as well as inconsistent clinical findings. The patient's medical history, laboratory results, and imaging studies were considered in the investigation. Heterophilic antibodies, likely developed during the SARS-CoV-2 infection, were identified as the probable cause of interference. The interference was confirmed through various methods, including dilution studies, blocking heterophilic antibodies, and comparing results with an alternative D-dimer method. This case highlights the importance of recognizing and addressing interference in D-dimer testing, emphasizing the need for collaboration between clinicians and laboratory specialists.

Interfering antibodies may contribute to elevated D-dimer: a case report

BACKGROUND

Plasma levels of D-dimer are elevated in patients with thromboembolisms. Here we investigated the existence of interfering antibodies as a potential cause for elevated D-dimer levels.

CASE PRESENTATION

A 42-year-old white Caucasian woman with a prior history of pulmonary embolism during her first pregnancy (treated with heparin therapy for 6 weeks postnatally) and hypothyroidism had a persistent elevated D-dimer without any clinical or ultrasound-based signs of thromboembolic conditions during her second pregnancy. We obtained informed consent and plasma was obtained from the patient. D-dimer levels were measured using two different assays. We also tested for the presence of rheumatoid factor, performed dilution series, and finally used an antibody depletion strategy. The two D-dimer assays performed similarly. Using our antibody depletion technique, we observed that ~ 1/3 of the increased plasma levels of D-dimer may be attributed to interfering antibodies.

CONCLUSIONS

Our results identify interfering antibodies as a potential contributor to an increased D-dimer in this patient. Our case highlights the potential of heterophilic interference for increased D-dimer and provides a procedure to determine this analytically.

Detection of polyreactive immunoglobulin G facilitates diagnosis in children with autoimmune hepatitis

OBJECTIVE

The detection of autoantibodies is essential to diagnose autoimmune hepatitis (AIH). Particularly in children, specificity of autoantibodies decreases due to lower titers being diagnostic and being present not only in AIH but also in other liver diseases. Recently, quantification of polyreactive IgG (pIgG) for detection of adult AIH showed the highest overall accuracy compared to antinuclear antibodies (ANA), anti-smooth muscle antibodies (anti-SMA), anti-liver kidney microsomal antibodies (anti-LKM) and anti-soluble liver antigen/liver pancreas antibodies (anti-SLA/LP). We aimed to evaluate the diagnostic value of pIgG for pediatric AIH.

DESIGN

pIgG, quantified using HIP1R/BSA coated ELISA, and immunofluorescence on rodent tissue sections were performed centrally. The diagnostic fidelity to diagnose AIH was compared to conventional autoantibodies of AIH in training and validation cohorts from a retrospective, European multi-center cohort from nine centers from eight European countries composed of existing biorepositories from expert centers (n = 285).

RESULTS

IgG from pediatric AIH patients exhibited increased polyreactivity to multiple protein and non-protein substrates compared to non-AIH liver diseases and healthy children. pIgG had an AUC of 0.900 to distinguish AIH from non-AIH liver diseases. pIgG had a 31-73% higher specificity than ANA and anti-SMA and comparable sensitivity that was 6-20 times higher than of anti-SLA/LP, anti-LC1 and anti-LKM. pIgG had a 21-34% higher accuracy than conventional autoantibodies, was positive in 43-75% of children with AIH and normal IgG and independent from treatment response.

CONCLUSION

Detecting pIgG improves the diagnostic evaluation of pediatric AIH compared to conventional autoantibodies, primarily owing to higher accuracy and specificity.

Pitfalls in the lab assessment of hypopituitarism

The diagnostic approach to hypopituitarism involves many disciplines. Clinical symptoms rarely are specific. Imaging techniques are helpful but cannot prove the specific functional defects. Therefore, the definitive diagnosis of pituitary insufficiency is largely based on laboratory tests. However, also laboratory methods come with inherent limitations, and it is essential for the clinician to know and recognize typical pitfalls. Most factors potentially impairing the quality of hormone measurements are introduced in the preanalytical phase, i.e. before the hormones are measured by the laboratory. For example, the timing of blood drawing with respect to circadian rhythm, stress, and medication can have an influence on hormone concentrations. During the actual analysis of the hormones, cross-reactions with molecules present in the sample presenting the same or similar epitopes than the intended analyte may affect immunoassays. Interference can also come from heterophilic or human anti-animal antibodies. Unexpected problems can also be due to popular nutritional supplements which interfere with the measurement procedures. An important example in this respect is the interference from biotin. It became only clinically visible when the use of this vitamin became popular among patients. The extreme serum concentrations reached when patients take it as a supplement can lead to incorrect measurements in immunoassays employing the biotin-streptavidin system. To some extent, hormone analyses using liquid chromatography mass spectrometry (LCMS) can overcome problems, although availability and cost-effectiveness of this method still imposes restrictions. In the post-analytical phase, appropriateness of reference intervals and cut-offs with respect to the specific analytical method used is of outmost importance. Furthermore, for interpretation, additional biological and pharmacological factors like BMI, age and concomitant diseases must be considered to avoid misinterpretation of the measured concentrations. It is important for the clinician and the laboratory to recognize when one or more laboratory values do not match the clinical picture. In an interdisciplinary approach, the search for the underlying cause should be initiated.

John Cunningham Virus and Progressive Multifocal Leukoencephalopathy: A Falsely Played Diagnosis

Progressive Multifocal Leukoencephalopathy (PML) is a possibly fatal demyelinating disease and John Cunningham Polyomavirus (JCPyV) is believed to cause this condition. The so-called JCPyV was initially reported in lymphoma and Human Immunodeficiency Virus (HIV) cases, whereas nowadays, its incidence is increasing in Multiple Sclerosis (MS) cases treated with natalizumab (Tysabri). However, there are conflicting literature data on its pathology and diagnosis, whereas some misdiagnosed reports exist, giving rise to further questions towards the topic. In reality, the so-called PML and the supposed JCPyV are not what they seem to be. In addition, novel and more frequent PML-like conditions may be reported, especially after the Coronavirus Disease 2019 (COVID-19) pandemic.

False diagnosis of recurrent thyroid carcinoma: the importance of testing for heterophile antibodies

Thyroglobulin (Tg) levels are important to predict recurrence in differentiated thyroid cancer patients.However, false-positive results can hence the request of unnecessary tests and treatments. We reported two cases of interference in thyroglobulin measurement and the workup to investigate them. Both patients achieved an excellent response to therapy after total thyroidectomy and one patient had also received radioiodine treatment. During the follow-up, Tg levels increased and there was no evidence of recurrent disease in the imaging studies. The Tg levels by the Access platform were positive but the results by Elecsys platform and LC-MS/MS were undetectable, leading to the hypothesis of heterophile antibodies (HAbs) interference. The possibility of HAbs interference must be considered when the Tg levels do not fit in the clinical picture. The measurement of Tg by another immunoassay or by LC-MS/MS may be useful in these situations.

Detecting the interferences in adrenocorticotropic hormone measurement - three cases reinforcing the efficiency of the complementary clinical and laboratory audit

Accurate measurement of adrenocorticotropic hormone (ACTH) is crucial in the evaluation of pituitary and adrenal disorders. Although great progress has been achieved in ACTH measurement with immunometric assays, interference may occur and adversely affect the clinical management. The report contributes to compiling the evidence on the clinical challenges with the management of the interferences in the ACTH measurement by presenting three cases: two with clinically overt hypercortisolism and discrepant ACTH concentrations within the reference interval; the third case describes the falsely elevated ACTH in a patient with secondary adrenal insufficiency. In all patients, the results obtained with the two immunometric platforms, chemiluminescence (CLIA) immunoassay (Siemens, Immulite) and electrochemiluminescence (ECLIA) immunoassay (Roche, Cobas), were discordant. Serial dilution of plasma samples revealed nonlinearity. After polyethylene glycol (PEG) precipitation recoveries were less than 22%, 26%, and 3%, respectively, supporting interference. Moreover, a decrease in ACTH concentration after incubation in a heterophile antibody-blocking tube was observed in the second case. In the first case, misinterpretation of ACTH led to inferior petrosal sinus sampling (IPSS), whereas timely detection of assay interference prevented further investigations in other cases. Increasing awareness regarding ACTH interference and comprehensive approach in evaluation could allow timely detection, helping to prevent unnecessary testing and perplexing clinical outcomes.

Immunoassay interferences: laboratory pitfall in the diagnosis of adrenocortical carcinoma

A woman in her late 50s with recent onset of hypertension, diabetes, lumbar pain and unintentional weight loss was diagnosed with a cortisol and androgen-producing adrenal mass. Despite this, serum adrenocorticotropic hormone (ACTH) concentration was inappropriately elevated, which was investigated thoroughly. Investigations included a brain magnetic resonance imaging to exclude concomitant pituitary adenoma, a corticotropin-releasing hormone stimulation test and a gallium-68 DOTATATE and 18F-FDOPA PET scan, both excluding ectopic ACTH production. Considering the disparity between clinical presentation and biochemical results, the ACTH was reanalysed using the Cobas immunoassay (Roche, Switzerland), ultimately unveiling the cause for ACTH elevation. ACTH levels had previously been measured with ACTH Immulite (Siemens, Germany), a two-site immunoassay which is prone to interferences causing falsely elevated ACTH concentrations. Inaccurate laboratory levels can lead to diagnosis delay and unnecessary diagnostic procedures and a close communication between the physicians and laboratorians is of utmost importance.

Clinical Biochemistry of Serum Troponin

Accurate measurement and interpretation of serum levels of troponin (Tn) is a central part of the clinical workup of a patient presenting with chest pain suspicious for acute coronary syndrome (ACS). Knowledge of the molecular characteristics of the troponin complex and test characteristics of troponin measurement assays allows for a deeper understanding of causes of false positive and false negative test results in myocardial injury. In this review, we discuss the molecular structure and functions of the constituent proteins of the troponin complex (TnT, TnC, and TnI); review the different isoforms of Tn and where they are from; survey the evolution of clinical Tn assays, ranging from first-generation to high-sensitivity (hs); provide a primer on statistical interpretation of assay results based on different clinical settings; and discuss potential causes of false results. We also summarize the advances in technologies that may lead to the development of future Tn assays, including the development of point of care assays and wearable Tn sensors for real-time continuous measurement.

Primary Sjogren's syndrome presenting as ptosis and eyelid swelling: A case report

Key Clinical Message

This unique case report of primary Sjogren's syndrome (pSS) shows bilateral ptosis and significant periorbital edema, compromising vision. To avoid misleading diagnosis, antibody tests must be evaluated and interpreted in the context of clinical findings.

Abstract

Primary Sjögren's syndrome is an idiopathic, autoimmune disorder involving the lacrimal and salivary glands characterized by both localized and systemic manifestations including xerostomia and keratoconjunctivitis sicca. Myasthenia Gravis (MG) is also an autoimmune disorder characterized by the development of auto-antibodies against nicotinic acetylcholine receptors that causes decreased muscle response to stimulation. It usually presents with ptosis and generalized body weakness. Ophthalmological involvement is common in both disorders but ptosis is very rarely seen in pSS. We report the case of a 27-year-old woman presenting to our clinic with the complaint of ptosis and eyelid swelling. She also had a positive anti-acetylcholine receptor antibody test and her initial presentation mimicked Myasthenia Gravis. Her autoimmune workup revealed a positive titer of Anti Ro SSA antibodies. Myasthenia Gravis was ruled out on electrodiagnostic studies which showed no decremental response, and pSS was confirmed on lip biopsy. Our case highlights that it is important to interpret the antibody test results in the context of clinical findings as we can have spurious results in autoimmune diseases. Autoimmune conditions can have varying presenting complaints hence, clinical judgment should always overrule diagnostic investigations and should thus guide patient management.

Evaluation of the analytical and clinical performance of a new high-sensitivity cardiac troponin I assay: hs-cTnI (CLIA) assay

OBJECTIVES

Cardiac troponin (cTn) is the key biomarker for diagnosis of acute coronary syndrome (ACS). We performed a complete assessment of the high-sensitivity cardiac troponin I (hs-cTnI) (CLIA) assay on the analytical performance and clinical diagnostic performance, which was compared with Abbott ARCHITECT hs-cTnI assay.

METHODS

Sex-specific 99th percentile upper reference limits (URLs) were determined from a healthy population of 424 males and 408 females. High-sensitivity performance was assessed by examining the imprecision at sex-specific URLs and the detectable results above LoD in a cohort of healthy population. The diagnostic performance of the hs-cTnI (CLIA) assay was validated in a population of 934 patients with suspected ACS.

RESULTS

The 99th percentile URLs were 15.3 ng/L for female, 31.3 ng/L for male and 24.2 ng/L for overall population. The total imprecision near the sex-specific 99th percentile URLs were <5 %. 76.74 % of females, 97.12 % of males and 86.69 % of overall population had cTnI values exceeding the LoD, which met the criteria of high-sensitivity troponin assay. No cross-reactivity or interference was identified. The diagnostic sensitivity, specificity, PPV, NPV, and AUC of hs-cTnI (CLIA) assay were 97.97 , 90.70, 79.02, 99.21 % and 0.9885, respectively, which were comparable to ARCHITECT hs-cTnI assay.

CONCLUSIONS

hs-cTnI (CLIA) assay is a high-sensitivity troponin I method with high precision, sensitivity and specificity. The clinical diagnostic performance of hs-cTnI (CLIA) is comparable to the established ARCHITECT hs-cTnI assay. Mindray's hs-cTnI (CLIA) assay is an attractive alternative for diagnosis of myocardial infarction with a high level of accuracy and safety.

Heterophilic Interference of Rheumatoid Factor in TSH Immunometric Assay: A Cross-Sectional Observational Study

Introduction

Considering the inherent vulnerability of immunoassays for heterophilic interference and the potential of Rheumatoid Factor (RF) to act as a heterophile-like antibody, we conducted this study to investigate if RF leads to any such heterophilic interference in seropositive rheumatoid arthritis (RA) patients. The study was done on the TSH assay as it is a noncompetitive, double antibody sandwich assay, which is known to be vulnerable to heterophilic interference.

Methods

In this cross-sectional observational study, eighty-four consecutive newly diagnosed RF-positive RA patients underwent TSH, Free T4, and anti-TPO estimation using the chemiluminescence technique (CLIA) on Siemens Immulite 1000 platform. The samples were screened for TSH interference using four methods: 1) analysis on a different platform, 2) assessment of linearity using doubling dilutions, 3) polyethylene glycol (PEG) precipitation, and 4) addition of a commercial blocker.

Results

Ten samples had a loss of linearity on serial dilution, indicating potential interference. After heterophile blocker treatment, five cases exhibited interference. One patient had diagnostic interpretation discordance on the second platform. No sample on PEG precipitation suggested the influence of antibodies. It is worth noting that even in cases where interference was suspected, the clinical interpretation was largely unaffected by the correction of TSH values based on mean dilution or measurement after heterophile blocker treatment.

Conclusion

RF can cause heterophilic interference in TSH immunoassays used commercially. However, in most cases, this interference does not affect clinical decision-making.

Multiple immunoassay interference in a patient with falsely elevated calcitonin

Calcitonin (CT) is a diagnostic and follow-up marker of medullary thyroid carcinoma. Heterophile antibodies (HAbs) may interfere during immunometric assay measurements and result in falsely high CT levels and different markers. A 50-year-old female patient was referred to our institution for elevated CT levels (3,199 pg/mL [0-11,5]). Physical examination and thyroid ultrasonography show no thyroid nodules. Because of the discrepancy between the clinical picture and the laboratory results, various markers and hormones were examined to determine whether there was any interference in the immunometric assay. Thyroglobulin (Tg) and Adrenocorticotropic hormone (ACTH) levels were also found inaccurately elevated. After precipitation with polyethylene glycol, CT, Tg, and ACTH levels markedly decreased, showing macro-aggregates. Also, serial dilutions showed non-linearity in plasma concentrations. Additionally, CT samples were pretreated with a heterophilic blocking tube before measuring, and the CT level decreased to < 0.1 pg/mL, suggesting a HAb presence. Immunoassay interference should be considered when conflicting laboratory data are observed. This may help reduce the amount of unnecessary laboratory and imaging studies and prevent patients from complex diagnostic procedures.

Lack of observed interference by therapeutic monoclonal antibodies in select commonly utilized immunoassays

BACKGROUND

Therapeutic monoclonal antibodies (tmabs) have been hypothesized to interfere with immunoassay measurements, although studies investigating this potential new class of interference are lacking. This study evaluated the effects of tmabs used in cancers ipilimumab (Bristol Myers Squibb), nivolumab (Bristol Myers Squibb), pembrolizumab (Merck) and autoimmune disorders adalimumab (AbbVie), infliximab (Janssen) and vedolizumab (Takeda) in common immunoassays used in the clinical laboratory.

METHODS

Residual sera from 10 randomly chosen patients were split into two tubes and spiked with same volume (approximately 5 % final volume) of either saline (control) or 6 tmabs (final concentration of 100 μg/mL each). Concentrations from sixteen analytes in 19 different assays were assessed: TSH (Roche and Beckman), free thyroxine (Roche and Siemens), cortisol (Beckman), Cancer Antigens (CA): CA19-9 (Beckman), CA15-3 (Roche), CA125 (Roche), and CA27.29 (Siemens), carcinoembryonic antigen (Beckman), alpha-fetoprotein (Beckman), thyroglobulin (Beckman) and thyroglobulin antibodies (Beckman), thyroid peroxidase antibody (Beckman), beta-human chorionic gonadotropin (Roche and Beckman), total prostate-specific antigen (Roche), parathyroid hormone (Roche) and antinuclear antibodies IgG (Werfen). The tmab spiked residual sera were compared with matched saline spiked sera and percent error was assessed against allowable total error defined from biological variation or CLIA limits.

RESULTS

None of the tested immunoassays were affected by the presence of the tmabs, in samples within or outside assay reference intervals. The median % error among all immunoassays ranged between -2.0% (for TSH) to 2.7% (for TPO Ab assay).

CONCLUSION

These findings demonstrate no detectable tmab interference for the assessed immunoassays using spiked preparations of the tmabs in residual human sera. The findings are limited to the tmabs and immunoassays studied here.

Frontotemporal Dementia, Where Do We Stand? A Narrative Review

Frontotemporal dementia (FTD) is a neurodegenerative disease of growing interest, since it accounts for up to 10% of middle-age-onset dementias and entails a social, economic, and emotional burden for the patients and caregivers. It is characterised by a (at least initially) selective degeneration of the frontal and/or temporal lobe, generally leading to behavioural alterations, speech disorders, and psychiatric symptoms. Despite the recent advances, given its extreme heterogeneity, an overview that can bring together all the data currently available is still lacking. Here, we aim to provide a state of the art on the pathogenesis of this disease, starting with established findings and integrating them with more recent ones. In particular, advances in the genetics field will be examined, assessing them in relation to both the clinical manifestations and histopathological findings, as well as considering the link with other diseases, such as amyotrophic lateral sclerosis (ALS). Furthermore, the current diagnostic criteria will be explored, including neuroimaging methods, nuclear medicine investigations, and biomarkers on biological fluids. Of note, the promising information provided by neurophysiological investigations, i.e., electroencephalography and non-invasive brain stimulation techniques, concerning the alterations in brain networks and neurotransmitter systems will be reviewed. Finally, current and experimental therapies will be considered.

Extending the dynamic range of biomarker quantification through molecular equalization

Precision medicine requires highly scalable methods of multiplexed biomarker quantification that can accurately describe patient physiology. Unfortunately, contemporary molecular detection methods are generally limited to a dynamic range of sensitivity spanning just 3-4 orders of magnitude, whereas the actual physiological dynamic range of the human plasma proteome spans more than 10 orders of magnitude. Current methods rely on sample splitting and differential dilution to compensate for this mismatch, but such measures greatly limit the reproducibility and scalability that can be achieved-in particular, the effects of non-linear dilution can greatly confound the analysis of multiplexed assays. We describe here a two-pronged strategy for equalizing the signal generated by each analyte in a multiplexed panel, thereby enabling simultaneous quantification of targets spanning a wide range of concentrations. We apply our 'EVROS' strategy to a proximity ligation assay and demonstrate simultaneous quantification of four analytes present at concentrations spanning from low femtomolar to mid-nanomolar levels. In this initial demonstration, we achieve a dynamic range spanning seven orders of magnitude in a single 5 µl sample of undiluted human serum, highlighting the opportunity to achieve sensitive, accurate detection of diverse analytes in a highly multiplexed fashion.

Indeterminate results of interferon gamma release assays in the screening of latent tuberculosis infection: a systematic review and meta-analysis

Objectives

We aimed to evaluate the indeterminate rate of interferon gamma release assays (IGRAs) in the detection of latent tuberculosis infection (LTBI).

Methods

On 15 November 2022, we searched the PubMed® (National Library of Medicine, Bethesda, MD, USA), Embase® (Elsevier, Amsterdam, the Netherlands), and Cochrane Library databases in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Two investigators independently extracted the study data and assessed their quality using a modified quality assessment of diagnostic accuracy studies (i.e., QUADAS-2) tool. A random-effects model was used to calculate pooled results.

Results

We included 403 studies involving 486,886 individuals and found that the pooled indeterminate rate was 3.9% (95% CI 3.5%-4.2%). The pooled indeterminate rate for QuantiFERON®-TB (QFT) was similar to that for T-SPOT®.TB (T-SPOT) [odds ratio (OR) = 0.88, 95% CI 0.59-1.32]; however, the indeterminate rate for a new generation of QFT (QFT-plus) was lower than that of T-SPOT (OR = 0.24, 95% CI 0.16-0.35). The indeterminate rate in the immunocompromised population was significantly higher than that in healthy controls (OR = 3.51, 95% CI 2.11-5.82), and it increased with the reduction of CD4+ cell count in HIV-positive patients. Children's pooled indeterminate rates (OR = 2.56, 95% CI 1.79-3.57) were significantly higher than those of adults, and the rates increased as the children's age decreased.

Conclusion

On average, 1 in 26 tests yields indeterminate IGRA results in LTBI screening. The use of advanced versions of the QuantiFERON-TB assay (QFT-plus), may potentially reduce the occurrence of an indeterminate result. Our study emphasizes the high risk of immunosuppression and young age in relation to indeterminate IGRA, which should receive more attention in the management of LTBI.

Systematic review registration

PROSPERO https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42020211363, CRD42020211363.

ELISA Essentials: Surfaces, Antibodies, Enzymes, and Substrates

The enzyme-linked immunosorbent assay is a powerful analytical tool for the assessment of the kind and quantity of specific analytes found within a biological sample. It is based upon the exceptional specificity of antibody recognition of its cognate antigen and the power of enzyme-mediated signal amplification for sensitivity. However, development of the assay is not without challenges. Here, we describe the essential components and features necessary to successfully prepare and carry out the ELISA format.

Thyroglobulin Assay Interferences: Clinical Usefulness of Mass-Spectrometry Methods

Context

Thyroglobulin autoantibodies (TgAbs) affect thyroglobulin immunometric assays (TgIMAs), causing falsely low results. Conversely, heterophilic antibodies (HAs) may cause falsely elevated results. Thyroglobulin (Tg) measurements by mass spectrometry (MS) resist antibody interference. The most effective use of TgIMA/TgMS in the evaluation of Tg remains unclear.

Objective

The objective of this work was to study the usefulness of TgMS vs TgIMA in the presence of Tg measurement interference by HA and TgAb.

Methods

In 163 thyroid cancer patients, Tg was postoperatively measured by TgIMA and TgMS. When TgIMA was elevated and TgMS undetectable, HA was assessed by serial dilution and pretreatment with HA blocking reagent. TgIMA and TgMS were compared in TgAb-positive patients with well-characterized clinical status.

Results

6 out of 45 cases with TgIMA >1 ng/mL had undetectable TgMS. HA interference was confirmed by serial dilution and HA blocking reagent addition. In TgAb-positive cases, TgIMA and TgMS were highly correlated (R² = 0.86). In patients with structural disease and TgAb, TgIMA and TgMS were detectable in 6/19 patients, and 9/19 cases, respectively. The TgMS concentration range in the 3 discrepant cases ranged from 0.5 to 2.0 ng/mL. Hence, the presence of TgAb was associated with inappropriately reduced Tg concentrations with both TgIMA and TgMS.

Conclusion

HA cause falsely elevated TgIMA with undetectable TgMS with significant frequency. TgMS can be used to rule out HA interference. Albeit resistant to TgAb in vitro, TgMS detects little Tg in patients with TgAb and structural disease. Hence, TgAb may reduce Tg concentrations in vivo. The implication is that no assay design may be able to overcome this problem. TgMS may not detect structural disease in TgAb-positive patients.

Assessing Immunogenicity of Biologic Drugs in Inflammatory Joint Diseases: Progress Towards Personalized Medicine

Biologic drugs have greatly improved treatment outcomes of inflammatory joint diseases, but a substantial proportion of patients either do not respond to treatment or lose response over time. Drug immunogenicity, manifested as the formation of anti-drug antibodies (ADAb), constitute a significant clinical problem. Anti-drug antibodies influence the pharmacokinetics of the drug, are associated with reduced clinical efficacy, and an increased risk of adverse events such as infusion reactions. The prevalence of ADAb differs among drugs and diseases, and the detection of ADAb also depends on the assay format. Most data exist for the tumor necrosis factor-alpha inhibitors infliximab and adalimumab, with a frequency of ADAb that ranges from 10 to 60% across studies. Measurement of ADAb and serum drug concentrations, therapeutic drug monitoring, has been suggested as a strategy to optimize therapy with biologic drugs. Although the recent randomized clinical Norwegian Drug Monitoring (NOR-DRUM) trials show promise towards a personalized medicine prescribing approach by therapeutic drug monitoring, several challenges remain. A plethora of assay formats, with widely differing properties, is currently used for measuring ADAb. Comparing results between different assays and laboratories is difficult, which complicates the development of cut-offs necessary for guidelines and the implementation of ADAb measurements in clinical practice. With the possible exception of infliximab, limited data on clinical relevance and cost effectiveness exist to support therapeutic drug monitoring as a routine clinical strategy to monitor biologic drugs in inflammatory joint diseases. The aim of this review is to provide an overview of the characteristics and prevalence of ADAb, predisposing factors to ADAb formation, commonly used assessment methods, clinical consequences of ADAb, and the potential implications of ADAb assessments for everyday treatment of inflammatory joint diseases.

Falsely Elevated Estradiol Results in a 62-Year-Old Male Patient

Falsely increased estradiol levels can lead to unnecessary tests and therapeutic interventions. Here, we present a case of a 62-year-old man with falsely elevated estradiol, which led to subsequent follow-up testing and prescriptions. Alternative immunoassay testing, in conjunction with Scantibodies' blocking reagents, polyethylene glycol precipitation, and liquid chromatography-tandem mass spectrometry confirmation demonstrated that the falsely elevated estradiol was due to the presence of macro-estradiol. This report emphasizes the importance of recognizing analytical interferences in immunoassays to appropriately manage subsequent testing and patient care.

Kinetic characterization of SPR-based biomarker assays enables quality control, calibration free measurements and robust optimization for clinical application

Biomarker measurements are essential for the early diagnosis of complex diseases. However, many current biomarker assays lack sensitivity and multiplexing capacity, work in a narrow detection range and importantly lack real time quality control opportunities, which hampers clinical translation. In this paper, we demonstrate a toolbox to kinetically characterize a biomarker measurement assay using Surface Plasmon Resonance imaging (SPRi) with ample opportunities for real time quality control by exploiting quantitative descriptions of the various biomolecular interactions. We show an accurate prediction of SPRi measurements at both low and high concentrations of various analytes with deviations <5% between actual measurements and predicted measurement. The biphasic binding sites model was accurate for fitting the experimental curves and enables optimal detection of heterophilic antibodies, cross-reactivity, spotting irregularities and/or other confounders. The toolbox can also be used to create a (simulated) calibration curve, enabling calibration-free measurements with good recovery, it allows for easy assay optimizations, and could help bridge the gap to bring new biomarker assays to the clinic.

On the Effect of Heterophilic Antibodies on Serum Levels of Cardiac Troponins: A Brief Descriptive Review

Serum levels of cardiac troponins can be increased both with myocardial damage and in the absence of myocardial damage. In the second case, this is due to the influence of false-positive factors, among which heterophilic antibodies play a significant role. Understanding the causes of the formation of heterophilic antibodies, the features and mechanisms of their effect on serum levels of cardiac troponins, is an important condition for interpreting a false-positive result due to the influence of heterophilic antibodies. This brief, descriptive review presents the causes of heterophilic-antibodies formation and discusses their effect on serum levels of cardiac troponins.

Falsely elevated serum estradiol in woman of reproductive age led to unnecessary intervention and delayed fertility opportunity: a case report and literature review

BACKGROUND

The optimal management of patients in reproductive endocrinology relies on the accuracy and validity of sex hormone assays. Endogenous or exogenous substances can compete with the analyte. This competition can result in interfering errors and falsely indicate elevated serum levels. Obvious interference in estradiol assays appears to occur rarely. Consequently, clinicians who are not familiar with the potential of interference could be misled. In addition to unnecessary investigations and interventions and severe mental stress, falsely elevated estradiol results can result in missed or delayed fertility opportunities.

CASE

A 28-year-old female with pregnancy demand was diagnosed with polycystic ovary syndrome, Hashimoto's thyroiditis and subclinical hypothyroidism. She was found to have persistently elevated levels of serum estradiol in the early follicular phase (between 527 and 642 pg/mL). Screening workup was performed for nearly 11 months to find the causes. Serum tumor biomarkers were normal. Abdominal and pelvic computed tomography were negative for adrenal or adnexal masses. A left mesosalpinx cyst and benign pathological results were achieved by laparoscopic surgery. Hormonal substances and dietary supplements were absent, as determined by dietary records. Ultrasound confirmed follicles could grow slowly and eventually ovulate. Falsely elevated estradiol levels were suspected due to the discrepancy among high estradiol levels, follicle growth and normal gonadotropin levels. Immunological interference by heterophile antibody was finally verified by two competitive chemiluminescent immunoassay platforms (estradiol levels in the early follicle phase: 619 pg/mL, Siemens ADVIA CENTAUR and 60 pg/mL, Beckman, DxI 800). Successful clinical pregnancy was eventually achieved by combining induced ovulation, ultrasound monitoring and intercourse guidance.

CONCLUSIONS

Analytical interference and laboratory error should be suspicious at first when the clinical characteristics contradict the laboratory results of serum hormones. Measuring serum estradiol with another immunoassay platform is an easy and non-time-consuming method to exclude the heterophile interfering.

Persistence of SARS-CoV-2 Antibodies in Vaccinated Health Care Workers Analyzed by Coronavirus Antigen Microarray

Recent studies provide conflicting evidence on the persistence of SARS-CoV-2 immunity induced by mRNA vaccines. Here, we aim to quantify the persistence of humoral immunity following vaccination using a coronavirus antigen microarray that includes 10 SARS-CoV-2 antigens. In a prospective longitudinal cohort of 240 healthcare workers, composite SARS-CoV-2 IgG antibody levels did not wane significantly over a 6-month study period. In the subset of the study population previously exposed to SARS-CoV-2 based on seropositivity for nucleocapsid antibodies, higher composite anti-spike IgG levels were measured before the vaccine but no significant difference from unexposed individuals was observed at 6 months. Age, vaccine type, or worker role did not significantly impact composite IgG levels, although non-significant trends towards lower antibody levels in older participants and higher antibody levels with Moderna vaccine were observed at 6 months. A small subset of our cohort were classified as having waning antibody titers at 6 months, and these individuals were less likely to work in patient care roles and more likely to have prior exposure to SARS-CoV-2.

Development of Alzheimer’s Disease Biomarkers: From CSF- to Blood-Based Biomarkers

In the 115 years since the discovery of Alzheimer’s disease (AD), our knowledge, diagnosis, and therapeutics have significantly improved. Biomarkers are the primary tools for clinical research, diagnostics, and therapeutic monitoring in clinical trials. They provide much insightful information, and while they are not clinically used routinely, they help us to understand the mechanisms of this disease. This review charts the journey of AD biomarker discovery and development from cerebrospinal fluid (CSF) amyloid-beta 1-42 (Aβ42), total tau (T-tau), and phosphorylated tau (p-tau) biomarkers and imaging technologies to the next generation of biomarkers. We also discuss advanced high-sensitivity assay platforms for CSF Aβ42, T-tau, p-tau, and blood analysis. The recently proposed Aβ deposition/tau biomarker/neurodegeneration or neuronal injury (ATN) scheme might facilitate the definition of the biological status underpinning AD and offer a common language among researchers across biochemical biomarkers and imaging. Moreover, we highlight blood-based biomarkers for AD that offer a scalable alternative to CSF biomarkers through cost-saving and reduced invasiveness, and may provide an understanding of disease initiation and development. We discuss different groups of blood-based biomarker candidates, their advantages and limitations, and paths forward, from identification and analysis to clinical validation. The development of valid blood-based biomarkers may facilitate the implementation of future AD therapeutics and diagnostics.

Clinical Spectrum of Adrenal Cushing's Syndrome and the Caution for Interpretation of Adrenocorticotrophic Hormone: A Single-Center Experience

To describe the differences in presentation, biochemistry, and radiological evaluation of various etiologies of adrenal Cushing's syndrome (CS) from a single center. To emphasize caution for interpretation of plasma adrenocorticotropic hormone (ACTH), as a spuriously unsuppressed ACTH level by immunometric assay may lead to therapeutic misadventures in adrenal CS.

DESIGN

 Retrospective, single-center, observational study.

METHODS

  Fifty-eight adrenal CS patients [Adrenocortical carcinoma (ACC), n=30; Adenoma (ACA), n=15; Primary pigmented nodular adrenocortical disease (PPNAD), n=10; ACTH independent macronodular adrenal hyperplasia (AIMAH), n=3) evaluated at a tertiary care center in western India between January 2006 to March 2020 were included. Data on demography, clinical evaluation, biochemistry, imaging, management, histopathology, and outcome were recorded in a standard format and analyzed.

RESULTS

  Cortisol secreting ACC presented at 38(1-50) years with abdominal mass in 26/30 (86.7%) and 16/30 (53.3%) had metastases at presentation. ACA with autonomous cortisol excess presented at 25(4.9-40) years with discriminating features of CS in 14/15 (93.3%), sex steroid production in 2/15, unenhanced HU <10 in only one, and relative washout >40% in 8/11 (72.7%). One ACA and eight ACC patients had plasma ACTH (by Siemens Immulite assay) > 20 pg/ml, despite hypercortisolemic state.

CONCLUSIONS

  Cortisol-secreting ACC and ACA most often present with mass effects and florid CS, respectively. Baseline HU has low sensitivity to differentiate cortisol-secreting ACA from ACC. Plasma ACTH measured by Seimens Immulite is often unsuppressed, especially in ACC patients, which can be addressed by measuring ACTH by more accurate assays.

Hormone Immunoassay Interference: A 2021 Update

Immunoassays are powerful qualitative and quantitative analytical techniques. Since the first description of an immunoassay method in 1959, advances have been made in assay designs and analytical characteristics, opening the door for their widespread implementation in clinical laboratories. Clinical endocrinology is closely linked to laboratory medicine because hormone quantification is important for the diagnosis, treatment, and prognosis of endocrine disorders. Several interferences in immunoassays have been identified through the years; although some are no longer encountered in daily practice, cross-reaction, heterophile antibodies, biotin, and anti-analyte antibodies still cause problems. Newer interferences are also emerging with the development of new therapies. The interfering substance may be exogenous (e.g., a drug or substance absorbed by the patient) or endogenous (e.g., antibodies produced by the patient), and the bias caused by interference can be positive or negative. The consequences of interference can be deleterious when clinicians consider erroneous results to establish a diagnosis, leading to unnecessary explorations or inappropriate treatments. Clinical laboratories and manufacturers continue to investigate methods for the detection, elimination, and prevention of interferences. However, no system is completely devoid of such incidents. In this review, we focus on the analytical interferences encountered in daily practice and possible solutions for their detection or elimination.

Quantification of polyreactive immunoglobulin G facilitates the diagnosis of autoimmune hepatitis

BACKGROUND AND AIMS

Detection of autoantibodies is a mainstay of diagnosing autoimmune hepatitis (AIH). However, conventional autoantibodies for the workup of AIH lack either sensitivity or specificity, leading to substantial diagnostic uncertainty. We aimed to identify more accurate serological markers of AIH with a protein macroarray.

APPROACH AND RESULTS

During the search for more-precise autoantibodies to distinguish AIH from non-AIH liver diseases (non-AIH-LD), IgG antibodies with binding capacities to many human and foreign proteins were identified with a protein macroarray and confirmed with solid-phase ELISAs in AIH patients. Subsequently, polyreactive IgG (pIgG) was exemplarily quantified by reactivity against human huntingtin-interacting protein 1-related protein in bovine serum albumin blocked ELISA (HIP1R/BSA). The diagnostic fidelity of HIP1R/BSA binding pIgG to diagnose AIH was assessed in a retrospective training, a retrospective multicenter validation, and a prospective validation cohort in cryoconserved samples from 1,568 adults from 10 centers from eight countries. Reactivity against HIP1R/BSA had a 25% and 14% higher specificity to diagnose AIH than conventional antinuclear and antismooth muscle antibodies, a significantly higher sensitivity than liver kidney microsomal antibodies and antisoluble liver antigen/liver pancreas antigen, and a 12%-20% higher accuracy than conventional autoantibodies. Importantly, HIP1R/BSA reactivity was present in up to 88% of patients with seronegative AIH and in up to 71% of AIH patients with normal IgG levels. Under therapy, pIgG returns to background levels of non-AIH-LD.

CONCLUSIONS

pIgG could be used as a promising marker to improve the diagnostic workup of liver diseases with a higher specificity for AIH compared to conventional autoantibodies and a utility in autoantibody-negative AIH. Likewise, pIgG could be a major source of assay interference in untreated AIH.

Troponin interference with special regard to macrocomplex formation

Biomarkers, such as troponin-T and troponin-I, are regarded as the gold standard laboratory parameter for diagnosing many cardiological diseases. These parameters have been approved for clinical use. Many cardiological guidelines recommend the analysis of troponins in the majority of cardiological disease diagnoses and to also gain prognostic information. Nonetheless, many medical circumstances could cause false troponin elevations. In this article, we focus on troponin artifacts, particularly macro-immune complex formation, as important interference factors. Therefore, we performed a literature search from 2006 to 06/2021.

Specificity of plasma oxytocin immunoassays: A comparison of commercial assays and sample preparation techniques using oxytocin knockout and wildtype mice

Oxytocin has garnered much interest due to its role in affective states, social behaviors, and diverse physiological functions. However, approaches for measuring endogenous oxytocin concentrations have generated considerable controversy and debate. Common procedures for measuring oxytocin often produce uncorrelated results, and the detected concentrations frequently vary across two orders of magnitude. These findings have led some researchers to argue that immunoassays of plasma oxytocin may be unreliable and nonspecific, particularly when samples are not first processed using an extraction procedure. Here, we assess the specificity of oxytocin immunoassays using plasma samples from wildtype (WT) and oxytocin knockout (KO) mice. Plasma samples from both genotypes were measured using immunoassay and were measured with or without a solid-phase extraction. Using a commercially available kit from Arbor Assays, we demonstrate that both techniques generate a clear contrast between genotypes, with wildtype samples containing high concentrations of oxytocin (unextracted mean = 468 pg/ml; extracted mean = 381 pg/ml), while knockout samples measured below the lower limit of detection. Analytical validations demonstrated good parallelism and spike recovery for both methods. Furthermore, the same wildtype samples measured with both procedures were highly correlated (r = 0.95), although unextracted samples measured at significantly higher concentrations (p = 2.0 ×10-7, Cohen's d = 2.65). To test the generalizability of these results across immunoassay kits, we performed additional assays with kits from Cayman Chemical and Enzo Life Sciences. The Cayman Chemical kit produced results similar to Arbor Assays with a clean signal differentiating WT and KO plasma, both with and without an extraction step. The Enzo kit also differentiated the genotypes, with correlation between extracted and unextracted samples, but was considerably more susceptible to interference without the extraction, as evidenced by false positive signal in KO plasma samples. The extent to which these results generalize to other species remains unknown and challenging to assess.

Asymptomatic elevated parathyroid hormone level due to immunoassay interference

BACKGROUND

Parathyroid hormone (PTH) measurement using immunoassays is inherently vulnerable to interferences due to the presence of different proteins such as heterophile antibodies, human anti-animal antibodies, auto-analyte antibodies, the rheumatoid factor, and others. The frequency of immunoassay interference can be as high as 6%. We report the case of a patient showing persistent high levels of PTH without impact on calcium and bone metabolism.

CASE PRESENTATION

The patient was a 59-year-old asymptomatic woman who consistently showed elevated PTH levels (385-482 pg/ml) using the Roche Elecsys (Cobas e-411) and ADVIA Centaur assays, with normal calcium, phosphorus, vitamin D, and renal function parameters. She had no history of fractures, nephrolithiasis, gastrointestinal complaints, renal insufficiency, or autoimmune diseases. Her physical examination revealed no abnormalities. Biomarkers of bone metabolism were within the reference range. To rule out falsely elevated PTH levels, we initially performed serial dilutions using both assays, which revealed nonlinearity. After a polyethylene glycol precipitation test, less than 10% of PTH was recovered from the supernatant. These results suggested the presence of heterophile antibodies as the cause of the falsely elevated PTH levels.

CONCLUSION

Physicians should be aware of this issue in order to avoid unnecessary clinical investigations and inappropriate treatments.

Blood-Based ATN Biomarkers of Alzheimer's Disease: A Meta-Analysis

BACKGROUND

The Amyloid Tau Neurodegeneration (ATN) framework was proposed to define the biological state underpinning Alzheimer's disease (AD). Blood-based biomarkers offer a scalable alternative to the costly and invasive currently available biomarkers.

OBJECTIVE

In this meta-analysis we sought to assess the diagnostic performance of plasma amyloid (Aβ40, Aβ42, Aβ42/40 ratio), tangle (p-tau181), and neurodegeneration (total tau [t-tau], neurofilament light [NfL]) biomarkers.

METHODS

Electronic databases were screened for studies reporting biomarker concentrations for AD and control cohorts. Biomarker performance was examined by random-effect meta-analyses based on the ratio between biomarker concentrations in patients and controls.

RESULTS

83 studies published between 1996 and 2020 were included in the analyses. Aβ42/40 ratio as well as Aβ42 discriminated AD patients from controls when using novel platforms such as immunomagnetic reduction (IMR). We found significant differences in ptau-181 concentration for studies based on single molecule array (Simoa), but not for studies based on IMR or ELISA. T-tau was significantly different between AD patients and control in IMR and Simoa but not in ELISA-based studies. In contrast, NfL differentiated between groups across platforms. Exosome studies showed strong separation between patients and controls for Aβ42, t-tau, and p-tau181.

CONCLUSION

Currently available assays for sampling plasma ATN biomarkers appear to differentiate between AD patients and controls. Novel assay methodologies have given the field a significant boost for testing these biomarkers, such as IMR for Aβ, Simoa for p-tau181. Enriching samples through extracellular vesicles shows promise but requires further validation.

Sensitive and quantitative detection of cardiac troponin I with upconverting nanoparticle lateral flow test with minimized interference

Measurement of cardiac troponin I (cTnI) should be feasible for point-of-care testing (POCT) to diagnose acute myocardial infarction (AMI). Lateral flow immunoassays (LFIAs) have been long implemented in POCT and clinical settings. However, sensitivity, matrix effect and quantitation in lateral flow immunoassays (LFIAs) have been major limiting factors. The performance of LFIAs can be improved with upconverting nanoparticle (UCNP) reporters. Here we report a new methodological approach to quantify cTnI using UCNP-LFIA technology with minimized plasma interference. The performance of the developed UCNP-LFIA was evaluated using clinical plasma samples (n = 262). The developed UCNP-LFIA was compared to two reference assays, the Siemens Advia Centaur assay and an in-house well-based cTnI assay. By introducing an anti-IgM scrub line and dried EDTA in the LFIA strip, the detection of cTnI in plasma samples was fully recovered. The UCNP-LFIA was able to quantify cTnI concentrations in patient samples within the range of 30-10,000 ng/L. The LoB and LoD of the UCNP-LFIA were 8.4 ng/L and 30 ng/L. The method comparisons showed good correlation (Spearman's correlation 0.956 and 0.949, p < 0.0001). The developed UCNP-LFIA had LoD suitable for ruling in AMI in patients with elevated cTnI levels and was able to quantify cTnI concentrations in patient samples. The technology has potential to provide simple and rapid assay for POCT in ED setting.

Real evidence to assess clinical testing interference risk (REACTIR): A strategy using real world data to assess the prevalence of interfering substances in patients undergoing clinical laboratory testing

INTRODUCTION

Laboratory test interferences can cause spurious test results and patient harm. Knowing the frequency of various interfering substances in patient populations likely to be tested with a particular laboratory assay may inform test development, test utilization and strategies to mitigate interference risk.

METHODS

We developed REACTIR (Real Evidence to Assess Clinical Testing Interference Risk), an approach using real world data to assess the prevalence of various interfering substances in patients tested with a particular type of assay. REACTIR uses administrative real world data to identify and subgroup patient cohorts tested with a particular laboratory test and evaluate interference risk.

RESULTS

We demonstrate the application REACTIR to point of care (POC) blood glucose testing. We found that exposure to several substances with the potential to interfere in POC blood glucose tests, including N-acetyl cysteine (NAC) and high dose vitamin C was uncommon in most patients undergoing POC glucose tests with several key exceptions, such as burn patients receiving high dose IV-vitamin C or acetaminophen overdose patients receiving NAC.

CONCLUSIONS

Findings from REACTIR may support risk mitigation strategies including targeted clinician education and clinical decision support. Likewise, adaptations of REACTIR to premarket assay development may inform optimal assay design and assessment.

The role of antibody-based troponin detection in cardiovascular disease: A critical assessment

Cardiovascular disease has remained the world's biggest killer for 30 years. To aid in the diagnosis and prognosis of patients suffering cardiovascular-related disease accurate detection methods are essential. For over 20 years, the cardiac-specific troponins, I (cTnI) and T (cTnT), have acted as sensitive and specific biomarkers to assist in the diagnosis of various types of heart diseases. Various cardiovascular complications were commonly detected in patients with COVID-19, where cTn elevation is detectable, which suggested potential great prognostic value of cTn in COVID-19-infected patients. Detection of these biomarkers circulating in the bloodstream is generally facilitated by immunoassays employing cTnI- and/or cTnT-specific antibodies. While several anti-troponin assays are commercially available, there are still obstacles to overcome to achieve optimal troponin detection. Such obstacles include the proteolytic degradation of N and C terminals on cTnI, epitope occlusion of troponin binding-sites by the cTnI/cTnT complex, cross reactivity of antibodies with skeletal troponins or assay interference caused by human anti-species antibodies. Therefore, further research into multi-antibody based platforms, multi-epitope targeting and rigorous validation of immunoassays is required to ensure accurate measurements. Moreover, with combination and modification of various latest technical (e.g. microfluidics), antibody-based troponin detection systems can be more specific, sensitive and rapid which could be incorporated into portable biosensor systems to be used at point-of care.

Hypeprolactinemia: still an insidious diagnosis

Hyperprolactinemia can have different causes: physiological, pharmacological, and pathological. When investigating the etiology of hyperprolactinemia, clinicians need to be aware of several conditions leading to misdiagnosis. The most popular pitfalls are: acute physical and psychological stress, macroprolactin, hook effect, even though antibodies interferences and biotine use have to be considered. A 52-year-old woman was referred to Endocrinology clinic for oligomenorrhoea and headache. She worked as a butcher. Hormonal evaluation showed very high PRL (305 ng/ml, reference interval: <24 ng/ml) measured with the ECLIA immunoassay analyzer Elecsys 170. The patient's pituitary MRI was normal and macroprolactin was normal. Hormonal workup showed LH: 71.5 mU/ml (2-10.9 mU/ml), FSH: 111.4 mU/ml (3.9-8.8 mU/ml), Estradiol: 110.7 pg/mL (27-122 pg/ml). Since an interference was suspected, the sample was sent to another laboratory using a different assay. After antibody blocking tubes treatment (Heterophilic Blocking Tube, Scantibodies) PRL was 28.8 ng/ml (reference interval < 29.2 ng/ml). Analytical interference should be suspected when assay results are not consistent with the clinical picture. Endogenous antibodies (EA) include heterophile, human anti-animal, autoimmune and other nonspecific antibodies, and rheumatoid factors, that have structural similarities and can cross-react with the antibodies employed by the immunoassay, causing hyperprolactinemia misdiagnosis. The patient's job (butcher), led us to suspect the presence of anti-animal antibodies. Clinicians should also carefully investigate the use of supplements. Biotin can falsely increase hormone concentration in competitive assays. Many clinicians are still not informed about these pitfalls that are not mentioned in some recent reviews on PRL measurement.

Can Plasma α-Synuclein Help Us to Differentiate Parkinson's Disease from Essential Tremor?

Background

Studies have revealed controversial results regarding the diagnostic accuracy of plasma α-synuclein levels in patients with Parkinson's disease (PD). This study was aimed to analyze the diagnostic accuracy of plasma α-synuclein in PD versus healthy controls and patients with essential tremor (ET).

Methods

In this cross-sectional study, we included de novo (n = 19) and advanced PD patients [OFF (n = 33), and On (n = 35) states], patients with ET (n = 19), and controls (n = 35). The total plasma α-synuclein levels were determined using an ELISA sandwich method. We performed adjusted multivariate regression analysis to estimate the association of α-synuclein levels with group conditions [controls, ET, and de novo, OFF and ON-PD]. We studied the diagnostic accuracy of plasma α-synuclein using the area under the curve (AUC).

Results

The plasma α-synuclein levels were higher in controls compared to PD and ET (p < 0.0001), discriminating de novo PD from controls (AUC = 0.74, 95% CI 0.60-0.89), with a trend towards in advanced PD (OFF state) from ET (AUC = 0.69, 95% CI 0.53-0.84).

Conclusions

This is the first study examining and comparing plasma α-synuclein levels in ET vs. PD and controls. Preliminary findings suggest that plasma α-synuclein levels might help to discriminate de novo and advanced PD from controls and ET.

Rheumatoid factor and falsely elevated results in commercial immunoassays: data from an early arthritis cohort

The aim of the study was to  assess RF cross-reactivity to animal antibodies used in immunoassays, and to test if selected commercial immunoassays are vulnerable to interference from RF, causing false test results. Our study included samples from patients with RF-positive rheumatoid arthritis (RA) and controls (patients with RF-negative RA and psoriatic arthritis), included in an early arthritis-cohort. Reactivity to mouse IgG1, mouse IgG2a, rabbit IgG, bovine IgG, sheep/goat IgG and human IgG was analysed using in-house interference assays. RF-positive sera with strong reactivity to mouse IgG1 were analysed in three commercial immunoassays. To reveal interference, results before and after addition of blocking aggregated murine IgG1 were compared. Samples from 124 RF-positive RA patients and 66 controls were tested. We found considerably stronger reactivity toward animal antibodies, particularly mouse IgG1 (73% vs. 12%) and rabbit IgG (81% vs. 6%), in sera from RF-positive RA-patients compared to controls (p < 0.001). After selecting samples for testing in commercial assays, interference was revealed in 6/30 sera in the Architect β-hCG assay, 7/10 sera in the 27-plex cytokine assays, and in 2/33 samples in the Elecsys Soluble Transferrin Receptor assay. Our study revealed considerable RF reactivity to animal antibodies used in immunoassays and RF was associated with falsely elevated results in immunoassays used in clinical care and research. Clinicians, laboratorians, researchers and assay manufacturers must be alert to the risk of falsely elevated test results in RF-positive RA patients.

False-positive and false-negative COVID-19 cases: respiratory prevention and management strategies, vaccination, and further perspectives

Introduction: A novel Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) was reported via nucleic acid identification in December, 2019. Accuracy of SARS-CoV-2 diagnostic assays has emerged as a major barrier to COVID-19 diagnosis, particularly in cases requiring urgent or emergent treatment.

Areas covered: In this review, we explore the major reasons for false-positive and false-negative SARS-CoV-2 test results. How clinical characteristics, specific respiratory comorbidities and SARS-CoV-2 vaccination impact on existing diagnostic assays are highlighted. Different COVID-19 management algorithms based on each test and limitations are thoroughly presented.

Expert opinion: The diagnostic accuracy and the capacity of every available assay, which need to be interpreted in the light of the background incidence of SARS-CoV-2 infection in the communities in which they are used, are essential in order to minimize the number of falsely tested cases. Automated testing platforms may enhance diagnostic accuracy by minimizing the potential for human error in assays’ performance. Prior immunization against SARS-CoV-2 impairs the utility of serologic testing of suspected COVID-19 cases. Future avenues of research to evaluate lung tissue innate immune responses hold promise as a target for research to optimize SARS-CoV-2 and future infections’ testing accuracy.