Pars Distalis and Pars Tuberalis Thyroid-Stimulating Hormones and Their Roles in Macro-Thyroid-Stimulating Hormone Formation

Thyroid-stimulating hormone (TSH) and thyroid hormone levels are standard parameters in blood analysis. However, the immunoassays employed may lead to false-positive or false-negative results when the sample contains certain materials that interfere with the assay. Macro-TSH, a complex of TSH with immunoglobulin or albumin, may cause apparently increased TSH concentrations. TSH is produced in the pars tuberalis (PT) of the pituitary gland and by thyrotrophs of the pars distalis (PD). It was found that variable glycosylation can render the molecule more strongly bound to antibodies or albumin in the blood, leading to the hypothesis that macro-TSH consists mainly of PT-TSH. Although less known than PD-TSH, PT-TSH plays an important role in the central regulation of thyroid metabolism. The present review summarizes the physiological function of human PT-TSH and its role in macro-TSH formation. The prevalence of macro-hyperthyrotropinemia, the structure of PT-TSH and macro-TSH, problems in the measurement of TSH, and the action of PT-TSH in animals with seasonal breeding are discussed. Despite the absence of a specific function of macro-TSH in the organism, the identification of macro-TSH is important for avoiding unnecessary treatment based on a falsified readout of increased TSH concentrations as numerous individual case reports describe.

Spurious Serum Hormone Immunoassay Results: Causes, Recognition, Management

For over 50 years, immunoassays have been extensively used to quantitate hormones in blood, other fluids and tissues. Each assay has its own sensitivity, specificity and other analytical components. Despite the differences between commercial products, these assays provide important clinical information about hormone levels in patients. However, inaccurate results can occur because of technical issues, as well as patient-specific factors that can interfere with immunoassay hormone measurements. The latter include excessive normal blood or serum components, the presence of cross-reacting substances, extremely high levels of hormones leading to the high-dose hook effect, and interference from a variety of endogenous factors such as human antibodies that interact with the assay components or high levels of biotin in the serum from exogenous ingestion. This article briefly reviews the sources and recognition of endogenous interference, and describes methods to determine the correct serum hormone concentration.

Interferences in immunoassays: review and practical algorithm

Immunoassays are currently the methods of choice for the measurement of a large panel of complex and heterogenous molecules owing to full automation, short turnaround time, high specificity and sensitivity. Despite remarkable performances, immunoassays are prone to several types of interferences that may lead to harmful consequences for the patient (e.g., prescription of an inadequate treatment, delayed diagnosis, unnecessary invasive investigations). A systematic search is only performed for some interferences because of its impracticality in clinical laboratories as it would notably impact budget, turnaround time, and human resources. Therefore, a case-by-case approach is generally preferred when facing an aberrant result. Hereby, we review the current knowledge on immunoassay interferences and present an algorithm for interference workup in clinical laboratories, from suspecting their presence to using the appropriate tests to identify them. We propose an approach to rationalize the attitude of laboratory specialists when faced with a potential interference and emphasize the importance of their collaboration with clinicians and manufacturers to ensure future improvements.

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.

Falsely diagnosed thyrotoxicosis caused by anti-streptavidin antibodies and pre-wash procedures

Background

Anti-streptavidin antibodies are causal determinants of analytical interference during Thyroid function tests, and numerous reports have detailed such interference, with anti-streptavidin antibodies attracting attention.

Case presentation

We conducted a straightforward investigation of interference due to anti-streptavidin antibodies, with a case of a 60-year-old Japanese man who consulted our department for inconsistencies between his clinical course and Thyroid function tests. Experiments were conducted using Cobas8000 e602, which employs assay procedures with pre-wash to evaluate FT4 and FT3 levels.

Conclusions

To our knowledge, this is the first published report to clearly investigate such interferences using a combination of polyethylene glycol precipitation, heterophilic blocking tube precipitation, streptavidin-coated magnetic particle precipitation, and different instruments with or without pre-wash. Clinicians should consider that interferences caused by anti-streptavidin antibodies could lead to a misdiagnosis of thyrotoxicosis. Moreover, discussions between laboratory specialists, clinicians, and manufacturers are required to identify interferences and avoid unnecessary examinations and inappropriate treatment.

Interference of anti-streptavidin antibodies: More common than we thought? In relation to six confirmed cases

Automated immunoassays are extensively used in routine laboratory diagnostics of endocrine disorders because of their advantages, such as high sensitivity, precision, and specificity. However, these methods are limited by the susceptibility of the immunochemical reaction to various interferences. They may present interferences related to the assay's design, for example, the endogenous presence of anti-streptavidin antibodies (ASA) in platforms that use the biotin-streptavidin interaction. To date, there have been few reports in the literature of interference from endogenous ASA. However, such antibodies would potentially lead to falsely decreased or increased results of hormones that can lead to incorrect diagnoses. We report six patients with unusual thyroid function tests, incongruent to their clinical findings. They present elevated concentrations of total T3 and T4 and TSH values within the reference range when measured at Cobas 8000® e801 module (Roche Diagnostics®). Neither patient had been taking biotin; however, all demonstrated the presence of ASA causing falsely high results on competitive assays and also falsely low results on sandwich assays. The hormone panel was also analyzed in the same samples using a different platform available in our laboratory: Cobas 6000® e601 module (Roche Diagnostics®). Nine samples were sent to an external laboratory to be measured with the chemiluminescent method: ADVIA Centaur® (Siemens® Healthcare Diagnostics). The interference seems to affect e801 module and competitive assays the most without affecting results obtained by this chemiluminescent method. This interference could potentially affect other assays performed on the same platform, such as ATPO and estradiol. Finally, laboratories should suspect the presence of interference when there is no correlation between the hormone profile and the patient's clinic. The biotin neutralization protocol demonstrated its effectiveness to eliminate ASA interference.

Evaluation of the necessity and the feasibility of the standardization of procalcitonin measurements: Activities of IFCC WG-PCT with involvement of all stakeholders

Procalcitonin (PCT) is an important biomarker for sepsis diagnosis and management. To date, there is no higher-order reference measurement procedure (RMP) and certified reference material to achieve global standardization of results and results traceability to the SI units. Although efforts have been made to harmonize PCT results, a number of comparison studies and external quality assessment (EQA) schemes show conflicting results regarding results comparability and to date, equivalence of PCT results across the assays remains questionable in absence of studies relying on commutable EQA materials. In this context, the IFCC initiated activities to fill these gaps through the creation of the working group on standardization of PCT assays that gathers experts from National Metrology Institutes, calibration laboratories, clinicians, biologists, EQA providers and assay manufacturers. Among the activities, a higher order RMP and commutable reference materials are under development to build a robust reference measurement system (RMS). A commutability study is being organized to identify EQA materials that are fit for purpose to reliably estimate the current comparability of PCT results. This work will make it possible to evaluate the necessity and the feasibility for establishing and maintaining a new RMS for PCT assays, if deemed necessary.

High-sensitivity methods for cardiac troponins: The mission is not over yet

The measurement of cardiac troponin (cTn) is recommended by all guidelines as the gold standard for the differential diagnosis of Acute Coronary Syndromes. The aim of this review is to discuss in details some key issues regarding both analytical and clinical characteristics of the high-sensitivity methods for cTn (hs-cTn), which are still considered controversial or unresolved. In particular, the major clinical concern regarding hs-cTn methods is the difficulty to differentiate the pathophysiological mechanism responsible for biomarker release from cardiomyocytes after reversible or irreversible injury, respectively. Indeed, recent experimental and clinical studies have demonstrated that different circulating forms of cTnI and cTnT can be respectively measured in plasma samples of patients with reversible or irreversible myocardial injury. Accordingly, a new generation of hs-Tn methods should be set up, based on immunometric immunoassays or chromatographic techniques, specific for circulating peptide forms more characteristics for reversible or irreversible myocardial injury. It is conceivable that this new generation of hs-cTn methods will complete the mission regarding the laboratory tests for specific cardiac biomarkers, started more than 20 years ago, which has already revolutionized the diagnosis, prognosis and management of patients with cardiac diseases.

Interference of anti-streptavidin antibodies in immunoassays: a very rare phenomenon or a more common finding?

Background

Anti-streptavidin antibodies (ASA) may cause analytical interference on certain immunoassay platforms. Streptavidin is purified from the non-pathogenic Streptomyces avidinii soil bacterium. In contrast to interference with biotin, ASA interference is supposed to be much rarer. In-depth studies on this topic are lacking. Therefore, we carried out an analysis toward the prevalence and the possible underlying cause of this interference.

Methods

Anti-streptavidin (AS)-immunoglobulin G (IgG) and AS-IgM concentrations were determined on multiple samples from two patients with ASA interference and on 500 random samples. On a subset of 100 samples, thyroid-stimulating hormone (TSH) was measured on a Cobas analyzer before and after performing a neutralization protocol which removes ASA. The relationship between the ratio of TSH after neutralization/TSH before neutralization and the ASA concentration was evaluated. Subsequently, an extract of S. avidinii colonies was analyzed using sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and immunoblotting.

Results

A positive correlation between AS-IgM concentrations and TSH ratio was obtained. Eight samples out of 500 exceeded the calculated AS-IgM cut-off value. In comparison to the AS-IgM concentrations in the population, titers from the two described cases clearly stood out. The isolated cases represent the end of a broader spectrum as there is a continuum of AS-IgM reactivity in the general population. We could not observe any differences in the immunoblot patterns between the cases and controls, which may indicate the general presence of ASA in the population.

Conclusions

Interference due to ASA is more prevalent than initially thought and is caused by IgM antibodies.

The Role of Interferences in the Increasing Incidence of Vitamin D Deficiency

OBJECTIVE

Lipemia is one of the causes of interference in immunoassay and LC-MS/MS methods. Increased prevalence of vitamin D deficiency in the US, where obesity is gradually increasing, raises the suspicion that high levels of fat diet and blood lipid levels interfere with vitamin D measurement results. The focus of this study was to investigate the effect of blood lipid profiles on vitamin D results and prevent the matrix effect.

MATERIAL AND METHODS

In this study, 25OH vitamin D3 (25OHD3) levels of 100 samples consecutively accepted to biochemistry laboratory regardless of age and sex were measured by the LC-MS/MS method, and each sample was restudied after 1/10 dilution. After dilution restudy, two groups were obtained-group 1 (results deviating below 20%) and group 2 (results deviating above 20%)-and the difference between the groups was investigated. There were 79 patients in group 1 and 21 patients in group 2. In our study, lipid profiles (triglyceride, total cholesterol, HDL, LDL) from the same samples of consecutive vitamin D patients were studied.

RESULTS

It was observed that the triglyceride, total cholesterol HDL, LDL, and 25OHD3 measurements of group 1 and group 2 were similar (p > 0.05). While the mean vitamin D value in the second group was 9.94 ± 7.85, the mean vitamin D value after dilution was measured as 39.23 ± 18.13 and was statistically significant. 25OHD3 concentrations of 21 patients out of 100 were found to be falsely low. Measurements were repeated to confirm the results.

CONCLUSION

The matrix effect caused by exogenous and endogenous interferences in the blood could be a hidden factor increasing the prevalence of vitamin D deficiency by causing falsely low 25OHD3 values. Suspicious results should be remeasured by a dilution study.

Biotin interference: evaluation of a new generation of electrochemiluminescent immunoassays for high-sensitive troponin T and thyroid-stimulating hormone testing

Background

Biotin is currently a matter of concern for laboratories using biotin-streptavidin-based immunoassays. Biotin interferences have been reported for high-sensitive troponin T (hsTnT) and thyroid-stimulating hormone (TSH) assays. We aimed to evaluate the new generation of hsTnT and TSH electrochemiluminescent immunoassays announced to be less sensitive to biotin.

Methods

Firstly, we assessed the analytical performances of new generation assays (imprecision, bias, total error, limit of quantification) and compared previous and new generation assays in the absence of biotin. Secondly, we challenged both generations of assays with samples spiked with seven different biotin levels. The efficiency of new generation assays was also compared to the streptavidin beads treatment.

Results

New generation assays presented suitable analytical performances. Previous and new generations of hsTnT and TSH assays were commutable in the absence of biotin. In the presence of biotin, we confirmed that previous generation assays were affected by biotin concentration as low as 40.5 ng/mL and that new generation assays were not affected up to the announced tolerance threshold of 1200 ng/mL. After the streptavidin beads treatment, we observed a higher imprecision for both parameters and a constant 10% negative bias for TSH compared to new generation assays.

Conclusions

New generation of electrochemiluminescent immunoassays appears as a reliable systematic solution to prevent biotin interference for hsTnT and TSH testing.

A practical approach towards the evaluation of aberrant thyroid function tests

Objective: To provide insight in patterns and causes of aberrant thyroid function tests (TFT) and to propose a practical approach for clinicians.Methods: Starting from an illustrative case report, an extensive literature search was performed, resulting in a narrative literature review.Results: TFT that cannot be explained by the negative feedback principle of the hypothalamo-pituitary-thyroid axis are a challenge for every clinician. Various alternative explanations for these TFT should be considered before drawing the conclusion of thyroid disorder, since incorrect diagnosis and treatment can have severe consequences for the patient.For example, the combination of elevated or normal TSH with elevated free T4 or T3 levels may result from the use of certain drugs or lab interference, while low or normal TSH with low T3 or T4 can often be explained by non-thyroidal illness or central hypothyroidism due to pituitary failure. Correct identification of these clinical situations requires understanding thyroid hormone metabolism and action, knowledge of some laboratory techniques, and a multistep evaluation process.Conclusion: To avoid incorrect diagnosis and thus treatment, clinicians should be aware of the existence of aberrant TFT and know how to decipher them.

Detection and characterization of estradiol (E2) and unconjugated estriol (uE3) immunoassay interference due to anti-bovine alkaline phosphatase (ALP) antibodies

Objectives

Competitive immunoenyzmatic assays for estradiol (E2) and unconjugated estriol (uE3) on UniCel DxI 800 Access immunoassay systems (Beckman Coulter) utilize bovine alkaline phosphatase (ALP) for amplification. In these assays, rare 'IND' error flags indicate that a relative light unit (RLU) raw result is past the high or low end of the calibration curve but cannot be differentiated from an instrument error or analytical interference. The present studies were conducted to establish a protocol to identify analytical interference and to characterize its mechanism when present.

Design and methods

Matrix and recovery studies were conducted to establish a protocol for interference identification. Spiking experiments with inactivated calf intestinal ALP were performed to determine whether interference could be blocked. Commercial anti-ALP antibodies (Abs) were spiked into human serum to model assay interference. Three E2 immunoassays which do not include ALP as a reagent component (cobas e602, Roche; Centaur XP, Siemens; ARCHITECT i2000_SR, Abbott) were tested for comparative purposes.

Results

1:2 dilution of specimen into Access Sample Diluent A (Beckman) differentiated IND error flags due to true low results (e.g. less than the analytical measurement range; AMR) from those due to assay interference. Interferences were reduced by pre-incubation with inactivated ALP and could be replicated by spiking with commercial anti-ALP Abs.

Conclusions

Patient anti-bovine ALP Abs can cause interference on DxI 800 E2 and uE3 assays. This model can be used to investigate interference risk with other ALP-dependent assays.

Heterophile antibody interference affecting multiple Roche immunoassays: A case study

BACKGROUND

Analysis of many clinically important analytes is dependent on antibody-based assays. However, depending on the design, these assays are vulnerable to interference from endogenous molecules including circulating antibodies and free biotin. In this case report, we describe a patient whose laboratory findings from immunoassay based methodologies, are inconsistent with the clinical presentation.

CASE PRESENTATION

A 14-year-old male was referred to Pediatric Endocrinology for suspected hyperthyroidism based on critically elevated free thyroxine (fT4) levels although clinical assessment was inconsistent with hyperthyroidism. Because repeat testing was discrepant, Endocrinology questioned the validity of the results prompting consultation with the laboratory to investigate the source of the inconsistent findings. Review of discordant results revealed that fT4 levels measured in laboratories utilizing Roche instrumentation were critically high, while results from laboratories using alternative platforms (i.e. Siemens Centaur) were within normal limits.

CONCLUSION

After a comprehensive evaluation which included testing of paired specimens on multiple platforms, measurement of serially diluted specimens and a formal evaluation for the presence of heterophile antibodies, it was determined that a heterophile antibody interference was the most likely cause of the aberrant results in this patient.

Falsely elevated plasma ACTH levels measured by the Elecsys assay related to heterophilic antibody in a case of secondary adrenocortical insufficiency

A 49-year-old woman with membranous nephropathy was referred to our hospital during the tapering of oral prednisolone, because of suspicion of primary adrenal insufficiency based on a plasma ACTH level of 399.1 pg/mL in the Elecsys assay and a serum cortisol level of 3.1 μg/dL. A rapid ACTH stimulation test revealed a suboptimal response, whereas a prolonged ACTH simulation test showed a sufficient increase in her urinary free cortisol. Also, big ACTH was not detected by gel exclusion chromatography. Therefore, we speculated that ACTH levels were falsely elevated due to some interference substances. Pretreatment of her plasma with either polyethylene glycol precipitation or a heterophilic blocking tube substantially reduced her ACTH values. When either the Immulite ACTH II or the TOSOH II ACTH was tried instead of the Elecsys ACTH, her plasma ACTH values turned out to be lower and appropriate for her clinical status. These results indicated that heterophilic antibodies interfered only with the Elecsys ACTH assay presumably by bridging the capture and tracer antibodies. To our knowledge, this is the first case in which the Elecsys ACTH assay yielded falsely elevated results. Regardless of the measurement system used, if there is a discordance between assay results and clinical findings, it should be considered to adopt additional procedures and/or another assay.

Interferences With Thyroid Function Immunoassays: Clinical Implications and Detection Algorithm

Automated immunoassays used to evaluate thyroid function are vulnerable to different types of interference that can affect clinical decisions. This review provides a detailed overview of the six main types of interference known to affect measurements of thyroid stimulating hormone (TSH), free thyroxine (T4) and free triiodothyronine (T3): macro-TSH, biotin, antistreptavidin antibodies, anti-ruthenium antibodies, thyroid hormone autoantibodies, and heterophilic antibodies. Because the prevalence of some of these conditions has been reported to approach 1% and the frequency of testing for thyroid dysfunction is important, the scale of the problem might be tremendous. Potential interferences in thyroid function testing should always be suspected whenever clinical or biochemical discrepancies arise. Their identification usually relies on additional laboratory tests, including assay method comparison, dilution procedures, blocking reagents studies, and polyethylene glycol precipitation. Based on the pattern of thyroid function test alterations, to screen for the six aforementioned types of interference, we propose a detection algorithm, which should facilitate their identification in clinical practice. The review also evaluates the clinical impact of thyroid interference on immunoassays. On review of reported data from more than 150 patients, we found that ≥50% of documented thyroid interferences led to misdiagnosis and/or inappropriate management, including prescription of an unnecessary treatment (with adverse effects in some situations), inappropriate suppression or modification of an ongoing treatment, or use of unnecessary complementary tests such as an I123 thyroid scan. Strong interaction between the clinician and the laboratory is necessary to avoid such pitfalls.

Diagnostic procedure in suspected Graves' disease

Diagnostic procedure in suspected Graves' disease has never been studied scientifically and actual practice seems quite variable, notably between countries. Recommendations are few and weak (expert opinion). This article presents the recommendations of an expert consensus meeting organized by the French Society of Endocrinology in 2016. In case of clinically suspected thyrotoxicosis, the first-line biological assessment is of thyroid-stimulating hormone (TSH). Free T4 and possibly free T3 assays assess biological severity and are necessary for treatment efficacy monitoring. Positive diagnosis of Graves' disease after biological confirmation of thyrotoxicosis does not always require complementary etiological examinations if clinical presentation is unambiguous, notably including extra-thyroid signs. Otherwise, first-line anti-TSH-receptor (TSH-R) antibody screening is recommended for its good intrinsic performance (sensitivity and specificity) and ease of access in France. Scintigraphy is reserved to rare cases of Graves' disease with negative antibody findings or when another etiology is suspected. Thyroid ultrasound scan may be contributive, but is not recommended in first line.

Apparent Hyperthyroidism Caused by Biotin-Like Interference from IgM Anti-Streptavidin Antibodies

BACKGROUND

Exclusion of analytical interference is important when there is discrepancy between clinical and laboratory findings. However, interferences on immunoassays are often mistaken as isolated laboratory artefacts. The mechanism of a rare cause of interference in two patients that caused erroneous thyroid function tests, and also affects many other biotin dependent immunoassays, was characterized and reported.

PATIENT FINDINGS

Patient 1 was a 77-year-old female with worsening fatigue while taking carbimazole over several years. Her thyroid function tests, however, were not suggestive of hypothyroidism. Patient 2 was a 25-year-old female also prescribed carbimazole for apparent primary hyperthyroidism. Despite an elevated free thyroxine, the lowest thyrotropin on record was 0.17 mIU/L. In both cases, thyroid function tests performed by an alternative method were markedly different. Further characterization of both patients' serum demonstrated analytical interference on many immunoassays using the biotin-streptavidin interaction. Sandwich assays (e.g., thyrotropin, follicle-stimulating hormone, troponin T, beta-human chorionic gonadotropin) were falsely low, while competitive assays (e.g., free thyroxine, free triiodothyronine, TSH binding inhibitory immunoglobulin) were falsely high. Pre-incubation of serum with streptavidin microparticles removed the analytical interference, initially suggesting the cause of interference was biotin. However, neither patient had been taking biotin. Instead, a ∼100 kDa immunoglobulin M (IgM) immunoglobulin with high affinity to streptavidin was isolated from each patient's serum. The findings confirm IgM anti-streptavidin antibodies as the cause of analytical interference.

SUMMARY

Two patients with apparent hyperthyroidism as a result of analytical interference caused by IgM anti-streptavidin antibodies are described.

CONCLUSION

Analytical interference identified on one immunoassay should raise the possibility of other affected results. Characterization of interference may help to identify other potentially affected immunoassays. In the case of anti-streptavidin antibodies, the pattern of interference mimics that due to biotin ingestion. However, the degree of interference varies between individual assays and between patients.

Anti-streptavidin IgG antibody interference in anti-cyclic citrullinated peptide (CCP) IgG antibody assays is a rare but important cause of false-positive anti-CCP results

Background:

The detection of anti-cyclic citrullinated peptide (anti-CCP) IgG antibodies in blood is mainly used for the diagnosis of rheumatoid arthritis. Falsely elevated anti-CCP IgG antibodies due to anti-streptavidin IgG antibodies were suspected in our laboratory.

Methods:

In this study, we evaluated, in a standardized approach, the prevalence of anti-streptavidin IgG antibodies in a primary care setting and the effect of anti-streptavidin IgG antibodies on anti-CCP IgG assays from three different important commercial manufacturers (Abbott, Roche Diagnostics, Thermo Fisher Scientific). Three different populations were consecutively and prospectively studied: serum samples from 1000 ambulatory patients, 286 serum samples from patients for which anti-CCP was requested and 89 serum samples from patients which had previously given a positive anti-CCP result on Architect® i2000.

Results:

The frequency of confirmed anti-streptavidin IgG-positive samples detected in this study was 0.6% (8/1375). Anti-CCP IgG was determined on the eight samples with confirmed anti-streptavidin IgG antibodies: with the Cobas® method, seven positive anti-CCP results were observed and five positive anti-CCP results with the Architect® method. No positive anti-CCP IgG results were obtained with the EliA™ method. Rheumatoid factor was negative in these eight samples.

Conclusions:

Anti-streptavidin IgG antibodies rarely cause false-positive results in some anti-CCP assays. However, despite being an infrequent assay problem, it could possibly lead to diagnostic confusion or even an incorrect diagnosis of rheumatoid arthritis.

Prevalence of biotin supplement usage in outpatients and plasma biotin concentrations in patients presenting to the emergency department

BACKGROUND

Several cases of biotin interference with laboratory testing have been reported in the literature. However, there are no publications discussing the extent of biotin use or plasma concentrations observed among the patient population. The objective of this study was to determine the prevalence of biotin consumption using two distinct methods: surveying the outpatient population using a questionnaire and quantifying biotin in plasma samples collected from patients presenting to the Emergency Department (ED).

METHODS

Survey questionnaires (n = 4000) were distributed to Mayo Clinic outpatients over one week (July 10-14, 2017). Biotin was quantified in residual waste plasma samples collected for physician-ordered electrolyte panels from patients presenting to the ED (March 6-12, 2017 and March 26-April 4, 2017, n = 1442 unique patient samples).

RESULTS

1944 patients (972 female, 963 male, 9 no answer) with a median (interquartile range) age of 62 (49-72) years returned completed questionnaires (48.6%). From the completed surveys, 7.7% (95% CI, 6.6-8.9%) indicated biotin use. Quantitation of biotin in plasma samples from ED patients (n = 1442) revealed that 7.4% (95% CI, 6.2-8.9%) had concentrations at or above the lowest known threshold (10 ng/mL) for biotin interference in Roche Diagnostics immunoassay tests.

CONCLUSIONS

According to our survey results, reported use of biotin was common. The range of biotin concentrations in ED patient samples highlights the magnitude of the biotin interference problem and identifies a population at risk for potential harm. These findings should guide laboratorians and clinicians in developing effective strategies to mitigate safety risks and in assessing biotin usage trends within their own patient populations.

Approach to the interpretation of unexpected laboratory results arising in the care of patients with inborn errors of metabolism (IEM)

Endocrinologists may encounter abnormal results in routine laboratory tests while caring for patients with inborn errors of metabolism. This article provides a framework for understanding these abnormalities as: a) part of the pathophysiology of the exceptional disease, b) exceptional laboratory errors related to the exceptional disease, or c) routine laboratory errors to which any patient sample is susceptible.

Population pharmacokinetics of exogenous biotin and the relationship between biotin serum levels and in vitro immunoassay interference

Aim: Biotin in human serum is a potential interfering factor for streptavidin-biotin-based assays. We aimed to evaluate the effective half-life of biotin and biotin metabolites, and establish a pharmacokinetic (PK) model to simulate the time taken for the biotin concentration to fall below a series of thresholds. Materials & methods: PK properties of biotin (5, 10 and 20 mg daily) were evaluated in healthy participants. Biotin serum concentrations were simulated for high-dose regimens (1 mg daily to 300 mg q.i.d.) using a population PK model. Results: Washout periods required for biotin concentrations to reach thresholds ranging from 10 to 100 ng/ml were successfully simulated. Conclusion: Our simulations provide valuable guidance on biotin washout periods necessary to avoid false assay results.

DIAGNOSIS OF ENDOCRINE DISEASE: Diagnostic approach to TSH-producing pituitary adenoma

Thyrotropin (TSH)-secreting adenomas (TSHomas) are the rarest form of pituitary adenomas, and most endocrinologists will see few cases in a lifetime, if any. In most cases, the diagnostic approach is complicated and cases may be referred after being presented as a syndrome of inappropriate TSH secretion or as a pituitary mass. This review aims to cover the past, present and possible future diagnostic approaches to TSHomas, including different clinical presentations, laboratory assessment and imaging advances. The differential diagnoses will be discussed, as well as possible coexisting disorders. By evaluating the existing reports and reviews describing this rare condition, this review aims to present a clinically practical suggestion on the diagnosic workup for TSHomas, Major advances and scientific breakthroughs in the imaging area in recent years, facilitating diagnosis of TSHomas, support the belief that future progress within the imaging field will play an important role in providing methods for a more efficient diagnosis of this rare condition.

Variability and Error in Cardiac Troponin Testing: An ACLPS Critical Review

OBJECTIVES

To provide a comprehensive overview of the complexities associated with cardiac troponin (cTn) testing. An emphasis is placed on the sources of error, organized into the preanalytical, analytical, and postanalytical phases of the testing pathway. Controversial areas are also explored.

METHODS

A case scenario and review of the relevant literature describing laboratory considerations involving cTn testing are described.

RESULTS

Advanced comprehension of the specific assay used in a given laboratory is necessary for optimal reporting, utilization, and quality monitoring of cTn.

CONCLUSIONS

cTn assays are reliable diagnostic tests for acute myocardial infarction, but understanding their limitations is required for appropriate result interpretation.

Depletion of biotin using streptavidin-coated microparticles: a validated solution to the problem of biotin interference in streptavidin-biotin immunoassays

Background Biotin interference in streptavidin-based immunoassays causes widespread analytical distortions that may lead to clinical confusion, inappropriate patient management and, ultimately, adverse events. Its prevalence has increased recently due to the increased use of high-dose biotin therapy in specific patient groups (notably multiple sclerosis) and possibly the general community. Methods We have developed a method to deplete biotin from samples using the streptavidin-coated magnetic microparticles that are a component of most susceptible assays. Results We show that high concentrations of spiked biotin can be adequately depleted from serum using this approach, and that gross biochemical derangements can be restored to normality. We also show that biotin in samples derived from multiple sclerosis patients receiving 300 mg biotin daily can be adequately depleted to remove associated analytical interference and restore normal results. The method is applicable to competitive and sandwich immunoassays and importantly, because it does not change the volume of the sample, suitable for the measurement of free thyroid hormone assays. Application of the method does not significantly change the precision of measurement, and for the majority of analytes, the accuracy is not substantially altered. Conclusions Adopting this method enables laboratories to confirm biotin interference in the appropriate clinical setting. Moreover, it enables laboratories to remove the interference and report accurate and reliable results, without the need for patients to withhold beneficial therapy prior to blood tests. Until the biotin tolerance of susceptible assays is improved, our method gives laboratories a safe alternative for reporting results using streptavidin-based methods.

Falsely Elevated Steroid Hormones in a Postmenopausal Woman Due to Laboratory Interference

Laboratory interference is a drawback in hormonal testing, and clinicians should have a high index of suspicion when faced with biochemical results discordant with the patient's clinical manifestations. A 62-year-old postmenopausal woman initially consulted her primary care physician for mood lability; laboratory workup showed markedly elevated levels of total serum estradiol, progesterone, testosterone, and cortisol as measured by immunoassay. Further investigation demonstrated no evidence of estrogen effect on uterus, no adrenal or adnexal mass, and no evidence of Cushing syndrome. Conventional techniques to unmask laboratory interference, such as dilution, antigen precipitation, and using a different immunoassay did not unveil a potential laboratory interference. The patient had no apparent risk factor for analytic interference, such as absent rheumatoid factor and heterophilic antibodies, but had only mild monoclonal IgG hypergammaglobulinemia. In this case, mass spectrometry unmasked the false elevation in steroid hormones. Interference of gammaglobulins or antibodies with the labeling and separation process of the assay could be the culprits. In conclusion, we report a unique case of multiple steroid hormones elevations due to laboratory interference unmasked by mass spectrometry.

False biochemical diagnosis of hyperthyroidism in streptavidin-biotin-based immunoassays: the problem of biotin intake and related interferences

Immunoassays are now commonly used for hormone measurement, in high throughput analytical platforms. Immunoassays are generally robust to interference. However, endogenous analytical error may occur in some patients; this may be encountered in biotin supplementation or in the presence of anti-streptavidin antibody, in immunoassays involving streptavidin-biotin interaction. In these cases, the interference may induce both false positive and false negative results, and simulate a seemingly coherent hormonal profile. It is to be feared that this type of errors will be more frequently observed. This review underlines the importance of keeping close interactions between biologists and clinicians to be able to correlate the hormonal assay results with the clinical picture.

Protein-based matrix interferences in ligand-binding assays

An adequate bioanalytical support for a typical biotherapeutic requires a number of assays, including those to measure drug concentration and to assess induction of specific immune responses. Ligand-binding assays are the most commonly used platform in bioanalysis of biotherapeutics. Ligand-binding assays are frequently designed to detect appropriate analytes in complex biological matrices with limited or no sample pretreatment steps. The complex composition of the test matrix is highly diverse and varies from normal to disease populations. Additional post-treatment changes are often observed, including induction of antidrug antibodies. Due to potential interaction of biological matrix components, for example, rheumatoid factors, heterophilic antibodies and human anti-animal antibodies, with the test analyte or assay reagents, ligand-binding assays are often subjected to various degrees of matrix interferences that lead to an erroneous under- or over-reporting of the analyte concentration. Impact of various matrix components and practical means designed to mitigate interferences are discussed in this Review.