Hook-effect in MAGLUMI immunoassay for serum anti-GAD antibodies in neurological disorders: When "wrong" matrix is the right choice

Antibodies against glutamic acid decarboxylase (anti-GAD) are a valuable diagnostic tool to detect severe autoimmune conditions as type 1 diabetes mellitus (T1DM) and anti-GAD related neurological disorders, having the latter more often anti-GAD concentrations in serum multiple times higher than in the former. Automated immunoassays, either with ELISA or chemiluminescent technology, are validated for diagnostic use in serum with analytical ranges suitable for T1DM diagnosis. In a patient presenting with a suspected autoimmune ataxia, anti-GAD testing on an automated chemiluminescent immunoassay (CLIA) resulted in slightly abnormal concentrations in serum (39.2 KIU/L) and very high concentrations in CSF (>280 KIU/L), thus prompting to proceed to serum dilutions to exclude a false negative result and a misdiagnosis. Different dilutions of serum resulted in nonlinear concentrations with endpoint result of 276,500 KIU/L at dilution 1:1000. CSF dilution was instead linear with endpoint result of 4050 KIU/L. In this case report we found that anti-GAD testing in CSF was essential to establish the clinical diagnosis and to suspect hook-effect in serum due to the excess of autoantibodies in this severe autoimmune condition.

Multicenter comparison of analytical interferences of 25-OH vitamin D immunoassay and mass spectrometry methods by endogenous interferents and cross-reactivity with 3-epi-25-OH-vitamin D3

Background

Vitamin D (vit-D) deficiency is highly prevalent in the Korean population, highlighting the need for accurate measurements. In this study, the interferences by endogenous and cross-reactive substances were compared between routine vit-D immunoassays and mass spectrometry (MS) methods.

Methods

Two MS methods and 4 immunoassays from different manufacturers (Abbott, Beckman Coulter, Roche, Siemens) were compared. Residual samples that were icteric, lipemic, hemolyzed, high in rheumatoid factor, from myeloma patients, or patients undergoing hemodialysis were collected. Also, 4 levels of National Institute of Standards and Technology (NIST) Standard Reference Material 972a, and 12 samples serially spiked with 3-epi-25-OH-D3 were prepared.

Results

Significant interferences were observed in hemolytic (Roche), icteric (Beckman and Siemens) and lipemic samples (all 4 immunoassays). Level 4 NIST material and 3-epi-25-OH-D3-spiked samples induced significant cross-reactivity, yielding higher total vit-D measurements in non-epimer-separating MS methods, and both the Beckman and Roche immunoassays.

Conclusion

Most observed interferences were consistent with manufacturers' claims, but overall improvement of immunoassay bias limits is required. Awareness of potential interference is important to increase the accuracy of vit-D measurements. Moreover, care is due when interpreting vit-D results of newborns, infants and less commonly, pregnant women, who are known to have physiologically high levels of the highly cross-reactive 3-epi-25-OH-D3.

Avoiding falsely low creatinine concentrations measured in patients treated with N-acetylcysteine for acetaminophen intoxication using enzymo-amperometric method - An in vitro and in vivo study

BACKGROUND

Circulating creatinine is a biomarker of paramount importance in clinical practice. In cases of acetaminophen (APAP) intoxication, the antidote, N-acetylcysteine (NAC), interferes with commonly used creatininase-peroxidase methods. This study aimed to assess whether creatininase-amperometric methods were affected in this context.

METHODS

This study includes in vitro interference tests, involving four creatinine assays using NAC-spiked plasma pools and an in vivo retrospective study comparing creatininase-peroxidase and creatininase-amperometric measurements in patients presenting with NAC-treated APAP poisoning.

RESULTS

Creatininase-peroxidase method was impacted by NAC interference in a clinically-significant manner at therapeutic NAC levels (basal value recovery of 80 % and 70 % for 500 and 1000 mg.L-1 of NAC, respectively), surpassing the desirable Reference Change Value (RCV%). Enzymo-amperometric methods were not impacted. Among patients, a mean bias of -45.2 ± 28.0 % was observed for the peroxidase detection method compared to the amperometric in those who received NAC prior plasma sampling and -2.7 ± 5.4 % in those who did not.

CONCLUSIONS

Our findings indicate that enzymo-amperometric creatinine assays remain unaffected by NAC interference due to the absence of the peroxidase step in the analytical process. Therefore, these methods are suitable to prevent spurious hypocreatininemia in APAP intoxicated patients undergoing NAC therapy.

Evaluation of local hemoglobinopathy prevalence and promotion of accurate hemoglobin A1c testing using historical data retrieval

OBJECTIVES

Heterozygous hemoglobin variants are known to cause method- and variant-specific interference with hemoglobin A1c (HbA1c) quantitation. Less attention has been paid to the role of other hemoglobin variants in confounding HbA1c testing. Here we evaluated the frequency with which enzymatic (ENZ) and immunoassay (IA) HbA1c quantitation methods, i.e., those unable to routinely detect the presence of hemoglobin variants, were used within our healthcare system for HbA1c analysis in patients with elevated fetal hemoglobin as well as compound heterozygous and homozygous variants.

DESIGN & METHODS

This analysis was enabled by automated review of HbA1c result history, implemented to promote detection of variants prior to HbA1c result reporting.

RESULTS

During a 54-week period, 319,290 HbA1c analyses were performed. We observed 110 unique patient cases (0.03% problem identification rate) in which HbA1c testing was ordered in the presence of either a homozygous or compound heterozygous hemoglobin variant or elevated hemoglobin F beyond the tolerance of the method. Among the 110 cases identified, 55 (50%) showed a compound heterozygous or homozygous hemoglobin variant while 55 (50%) showed elevated hemoglobin F. Of those cases involving a compound heterozygous or homozygous variant, 8/55 (15%) involved patients who had one or more ENZ or IA HbA1c results reported previously within our system. Of the 55 total compound heterozygous or homozygous variants identified, 37 (67%) were hemoglobin E, 10 (18%) hemoglobin S/C, 4 (7%) hemoglobin S, 2 (4%) hemoglobin C, 1 (2%) hemoglobin Camden, and 1 (2%) unidentified variant.

CONCLUSIONS

Exclusive use of methods unable to routinely detect the presence of hemoglobin variants may lead to reporting of HbA1c results that are not clinically meaningful.

Hydroxocobalamin infusion in a patient monitored for plasma free hemoglobin levels

Hemolysis is one of the most common preanalytical concerns in the clinical laboratory. Hydroxocobalamin administration causes red pigmentation of plasma that may mimic hemolysis and may interfere with chemistry assays. A male patient in his sixties was placed on extracorporeal membrane oxygenation (ECMO) as a bridge to transplantation. Daily plasma free hemoglobin measurements were ordered to monitor for adverse ECMO events. An intensely red plasma specimen was inconsistent with modestly elevated hemoglobin levels and became pink on dilution. Follow-up with providers indicated that the red plasma could be attributed to hydroxocobalamin administration. Performance of scanning spectrophotometry and assessment of a sample spiked with hydroxocobalamin indicated that the red colored hydroxocobalamin did not interfere with our 3,3',5,5'-tetramethylbenzidine based methodology for free plasma hemoglobin measurement. It is important for the laboratory professionals to be aware of the possibility of interference in hemoglobin assays due to hydroxocobalamin.

Ropinirole metabolite mimics a new psychoactive substance (4-HO-MET) in LC-MS/MS

Liquid chromatography tandem mass spectrometry (LC-MS/MS) is often regarded as a highly reliable methodology for confirmatory testing in analytical toxicology, especially for detection of new psychoactive substances (NPS) by clinical and forensic laboratories. However, false positives still do occur and erroneous reporting can have substantial legal implications. In this study, we investigated into the mechanism behind a clinically implausible, but apparently analytically sound, finding of a NPS (4-hydroxy-N-methyl-N-ethyltryptamine; 4-HO-MET) in a urine specimen for toxicology screening by LC-MS/MS. We discovered that a ropinirole metabolite (N-despropyl-ropinirole) was the culprit of interference as it shares high structural similarities with 4-HO-MET. The chemical similarities eluded various rigorous regulatory guidelines for compound identification utilizing computer-aided spectral library matching. After careful scrutiny of the mass spectra and comparison with a reference specimen, the compound was correctly identified. Our findings emphasize the important synergy between scientists and pathologists in considering the clinical context, especially drug history, in clinical and forensic toxicology analysis on biological specimens. Mass spectra should be reviewed for relative ion ratios in case of doubt. Understanding drug metabolism is essential for troubleshooting and result interpretation.

Plasma creatinine below limit of quantification in a patient with acute kidney injury

BACKGROUND

Acute kidney injury (AKI) is an infrequent complication of inflammatory bowel disease and can be exceptionally linked to interstitial nephritis secondary to anti-inflammatory drugs, such as Pentasa® (5-ASA).

CASE PRESENTATION

We present an case of an 80-year-old man who presented chronic diarrheas treated by Pentasa®. He developed AKI, evidenced by high plasma creatinine dosed in his local laboratory. At the hospital admission, plasma creatinine was exceptionally undetectable by the enzymatic method while Jaffe's method successfully determined it. Creatinine measurement by the enzymatic method was gradually restored during hospital stay, concomitant with the discontinuation of 5-ASA administration, suggesting that this drug could interfere with creatinine enzymatic assay. Creatinine enzymatic assays combine serial reactions. The last one called Trinder reaction, catalyzed by a peroxidase, uses H₂O₂ to convert uncolored dye in a colored compound, proportionally to creatinine concentration. We showed that AKI related-plasma accumulation of 5-ASA, could participate in the negative interference observed on creatinine measurement, by scavenging H₂O₂. Interestingly, all Trinder reaction-based measurements (uric acid, lipase, lactate, triglycerides and cholesterol) were affected. Negative interference of 5-ASA was confirmed by interferogram experiments on all Trinder reaction-dependent assays.

CONCLUSION

All Trinder-dependent parameters should be interpreted with the patient's treatment knowledge, in particular salicylate derivatives.

Determination of clinically acceptable cut-offs for hemolysis index: An application of bootstrap method using real-world data

OBJECTIVES

To assess the impact of hemolysis on laboratory results under local conditions and to verify the hemolysis index cut-off for potassium using real-world data.

METHODS

The statistical bootstrapping method was performed on 54,125 samples collected at the University Hospital of Örebro (USÖ). The results were compared to a method based on stratification of samples according to hemolysis level, and on paired difference testing.

RESULTS

Setting the acceptable allowable limit of error to 10%, the three assessed strategies yielded comparable results with respect to the impact of haemolytic interference on test results for potassium. The suggested cut-offs were 111 mg Hb/dL for the bootstrapping method, between 125-150 mg Hb/dL for the method based on stratification, and around 150 mg/dL for the paired difference testing strategy. The impact of hemolysis on potassium measurement is likely different between primary care patients and inpatients.

CONCLUSIONS

Using the effect of hemolysis on potassium measurement as a model, a novel approach towards finding clinically acceptable limits for analytical interference is presented, that relies on the bootstrapping method and on actual patient data from routine laboratory operation, hence incorporating local population characteristics, equipment and instrumental settings.

Hydroxocobalamin interference in routine laboratory tests: Development of a protocol for identifying samples and reporting results from patients treated with CyanokitTM

OBJECTIVES

Hydroxocobalamin (OHCob) is an antidote for cyanide poisoning in patients rescued from house fires and is known to cause interference with certain laboratory tests. Consensus is lacking on the extent of this interference and on how to handle these samples. The objectives of this study were to characterize OHCob interference across a wide range of laboratory tests and to develop protocols for identifying and reporting these samples.

DESIGNS & METHODS

Patient plasma samples (n = 5) were spiked with OHCob (1.5 mg/mL) and compared to controls without this drug. A series of analytes were measured using chemistry, urinalysis, coagulation, hematology, and blood gas instruments. Dose-response testing was performed on a subset of assays that showed interferences ≥10%.

RESULTS

Of the 77 analytes evaluated, 27 (35%) showed interference from OHCob, with chemistry and coagulation analytes showing the greatest effects. Of those affected, 22 analytes had a positive interference, whereas 5 analytes had negative interference. Dose-response studies showed dose-dependent increases and/or decreases consistent with initial spiking studies. Although red in colour, plasma samples with OHCob did not trigger hemolysis index flags, necessitating a special sample identification and reporting protocol.

CONCLUSION

OHCob had significant effects on several analytes across different instruments. These findings led to the development of special sample handling and reporting protocols to identify OHCob samples and ensure only accurate results are released. It is vital for emergency departments to document and notify their laboratories whenever blood samples from these patients are drawn.

Erroneously High Lactate: A Guide to Diagnosing Ethylene Glycol Poisoning

A high lactic acid level in critically ill patients is a marker of poor prognosis. However, lactic acidosis in ethylene glycol (EG) poisoning should be interpreted cautiously as analytical interference is observed with EG metabolites.

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.

Critical assessment of the ubiquitous occurrence and fate of the insect repellent N,N-diethyl-m-toluamide in water

The insect repellent diethyltoluamide (DEET) is among the most frequently detected organic chemical contaminants in water across a wide range of geographies from around the world. These observations are raising critical questions and increasing concerns regarding potential environmental relevance, particularly when the emergence of severe neurological conditions attributed to the Zika virus has increased the use of insect repellents. After dermal application, DEET is washed from the skin when bathing and enters the municipal sewer system before discharge into the environment. Mainly measured by gas chromatography or liquid chromatography coupled to mass spectrometry (GC-MS or LC-MS), more than 200 peer-reviewed publications have already reported concentrations of DEET ranging ng/L to mg/L in several water matrices from North America, Europe, Asia, Oceania, and more recently Africa and South America. While conventional wastewater treatment technology has limited capacity of removal, advanced technologies are capable of better attenuation and could lower the environmental discharge of organic contaminants, including DEET. For instance, adsorption on activated carbon, desalinating membrane processes (nanofiltration and reverse osmosis), ozonation, and advanced oxidation processes can achieve 50% to essentially 100% DEET attenuation. Despite the abundant literature on the topic, the ubiquity of DEET in the environment still raises questions due to the apparent lack of obvious spatio-temporal trends in concentrations measured in surface water, which does not fit the expected usage pattern of insect repellents. Moreover, two recent studies showed discrepancies between the concentrations obtained by GC-MS and LC-MS analyses. While the occurrence of DEET in the environment is well established, the concentrations reported should be interpreted cautiously, considering the disparities in methodologies applied and occurrence patterns observed. Therefore, this manuscript provides a critical overview of the origin of DEET in the environment, the relevant analytical methods, the occurrence reported in peer-reviewed literature, and the attenuation efficacy of water treatment processes.

Hypercalcemia and elevated concentration of vitamin D: A case report too easy to be true

BACKGROUND

Endogenous (heterophile, human anti-animal …) antibodies are a known cause of interference in immunoassays.

CASE REPORT

A patient with hypercalcemia and low PTH levels was investigated. The serum 25OH vitamin D (25OHD) concentration was above the analytical range of the automated analyser (>150ng/mL) but serum dilutions were not linear. A myeloma-related monoclonal peak of immunoglobulin G (30g/L) was found.

RESULTS

Alternative 25OHD assays (RIA, automated analysers, mass spectrometry) all found concentrations <25ng/mL. NabTM columns (Thermo Scientific) eliminated the endogenous immunoglobulin from the serum thus allowing the initial analyser to provide correct results.

DISCUSSION AND CONCLUSION

The potentially misleading point was that the apparent very high 25OHD levels were concomitant with hypercalcemia and low PTH levels thus mimicking vitamin D intoxication. Identifying assay interferences requires clinical awareness but, when suspected, one should be aware that technical tools or alternate assays are available to correct some interferences, including monoclonal immunoglobulins.