Identifying and reducing potentially wrong immunoassay results even when plausible and "not-unreasonable"

Substance P/calcitonin gene-related peptide and their receptors expression in human periodontal ligament after root canal preparation with five different systems

AIM

The purpose of this study was to quantify the effect of five different root canal preparation instruments on Substance P (SP), Calcitonin gene-related peptide (CGRP) and their receptors expression in healthy human periodontal ligament.

METHODOLOGY

STROBE guidelines were used to design a study using 60 periodontal ligament samples obtained from healthy lower premolars where extraction was indicated for orthodontic reasons. Prior to extraction 40 of these premolars were equally divided into four groups and root canals were prepared using different systems: Mtwo, Reciproc Blue, HyFlex EDM and Plex-V. Ten premolars were prepared with hand files and served as a positive control group. The remaining 10 premolars where extracted without treatment and served as a negative control group. All periodontal ligament samples were processed to measure the expression of SP, CGRP and their receptors by radioimmunoassay. Kruskal-Wallis and Duncan tests were performed to determine statistically significant differences between the groups for each variable.

RESULTS

Greater expression of all the peptides measured were found in the hand-file preparation group, followed by the Reciproc Blue, Mtwo, HyFlex EDM and Plex-V groups. The lower SP, CGRP and their receptors values were for the intact teeth control group. Kruskal-Wallis test showed statistically significant differences amongst groups (p < .001). Dunn post-hoc tests showed statistically significant differences in SP, CGRP and their receptors expression between the intact teeth and the hand-file and Reciproc Blue groups. Hand-file group showed significant differences with the other groups, except with Reciproc Blue, where no differences were observed in any of the peptides measured. Finally, no differences were observed between Plex-V and HyFlex in any of the peptides measured.

CONCLUSIONS

Root canal preparation with hand files and Reciproc Blue generates the highest expression of SP, CGRP, NK1 and CGRP1R in human periodontal ligament, whilst Plex-V and HyFlex maintain the basal expression of neuropeptides and their receptors. Mtwo showed intermediate results between Reciproc Blue and HyFlex.

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.

Macro-GH - a clinical entity causing a diagnostic challenge - a case report

AIM

Presentation of a new case of a patient with macro-GH, that may interfere with different GH assays leading to false-positive results in serum samples.

CASE PRESENTATION

A 61-year-old female was referred with a pituitary macroadenoma and elevated growth hormone levels The laboratory tests showed increased fasting GH level, measured by a sandwich chemiluminescence immunoassay (LIAISON® XL) without suppression on oral glucose tolerance test and normal IGF-1. The patient did not have the typical signs and symptoms of acromegaly. The patient underwent a transsphenoidal resection of a pituitary tumor, showing only α-subunit immunostaining. Postoperative GH levels remained elevated. An interference in the determination of GH level was suspected. GH was analyzed by three different immunoassays, UniCel DxI 600, Cobas e411 and hGH-IRMA. Heterophilic antibodies and rheumatoid factor were not detected in serum sample. GH recovery after precipitation with 25% polyethylene glycol (PEG) was 12%. Size-exclusion chromatography confirmed the presence of macro-GH in serum sample.

CONCLUSION

If results of laboratory tests are not consistent with the clinical findings, the presence of an interference within immunochemical assays could be suspected. To identify interference caused by the macro-GH, the PEG method and size-exclusion chromatography should be used.

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.

Understanding and managing interferences in clinical laboratory assays: the role of laboratory professionals

The recently raised concerns regarding biotin interference in immunoassays have increased the awareness of laboratory professionals and clinicians of the evidence that the analytical phase is still vulnerable to errors, particularly as analytical interferences may lead to erroneous results and risks for patient safety. The issue of interference in laboratory testing, which is not new, continues to be a challenge deserving the concern and interest of laboratory professionals and clinicians. Analytical interferences should be subdivided into two types on the basis of the possibility of their detection before the analytical process. The first (type 1) is represented by lipemia, hemolysis and icterus, and the second (type 2), by unusual constituents that are not undetectable before analysis, and may affect the matrix of serum/plasma of individual subjects. Type 2 cannot be identified with current techniques when performing the pre-analytical phase. Therefore, in addition to a more careful evaluation and validation of the method to be used in clinical practice, the awareness of laboratory professionals should be raised as to the importance of evaluating the quality of biological samples before analysis and to adopt algorithms and approaches in the attempt to reduce problems related to erroneous results due to specific or non-specific interferences.

Cardiac troponins: are there any differences between T and I?

The most recent international guidelines recommend the measurement of cardiac troponin I (cTnI) and cardiac troponin T (cTnT) using high-sensitivity methods (hs-cTn) for the detection of myocardial injury and the differential diagnosis of acute coronary syndromes. Myocardial injury is a prerequisite for the diagnosis of acute myocardial infarction, but also a distinct entity. The 2018 Fourth Universal Definition of Myocardial Infarction states that myocardial injury is detected when at least one value above the 99th percentile upper reference limit is measured in a patient with high-sensitivity methods for cTnI or cTnT. Not infrequently, increased hs-cTnT levels are reported in patients with congenital or chronic neuromuscular diseases, while the hs-cTnI values are often in the normal range. Furthermore, some discrepancies between the results of laboratory tests for the two troponins are occasionally found in individuals apparently free of cardiac diseases, and also in patients with cardiac diseases. In this review article, authors discuss the biochemical, pathophysiological and analytical mechanisms which may cause discrepancies between hs-cTnI and hs-cTnT test results.

Characterization of canine anti-mouse antibodies highlights that multiple strategies are needed to combat immunoassay interference

Immunoassays are widely used for detection and quantification of analytes in biological samples, but are vulnerable to analytical errors caused by interfering sample substances. Of particular interest are endogenous anti-animal antibodies that may bind to the immunoassay antibodies and cause erroneous test results. This phenomenon is a hazard to patient safety in both human and veterinary medicine. Here, we demonstrate that anti-mouse antibodies in dogs bind selectively to different regions of the murine IgG molecule, cross-react with IgG from different species, and consist of all major antibody classes present in canine serum (IgA, IgG and IgM). The antibody characteristics varied among individuals and their prevalence differed between two dog breeds. The selective binding to different IgG regions suggests that the antibodies might not originate from immunization through exposure to mice or other species. These findings show that canine anti-mouse antibodies are highly heterogeneous in nature and therefore require a combination of strategies to be counteracted.

Recent advances in immunodiagnostics based on biosensor technologies-from central laboratory to the point of care

Immunological methods are widely applied in medical diagnostics for the detection and quantification of a plethora of analytes. Associated analytical challenges usually require these assays to be performed in a central laboratory. During the last several years, however, the clinical demand for rapid immunodiagnostics to be performed in the immediate proximity of the patient has been constantly increasing. Biosensors constitute one of the key technologies enabling the necessary, yet challenging transition of immunodiagnostic tests from the central laboratory to the point of care. This review is intended to provide insights into the current state of this transition process with a focus on the role of biosensor-based systems. To begin with, an overview on standard immunodiagnostic tests presently employed in the central laboratory and at the point of care is given. The review then moves on to demonstrate how biosensor technologies are reshaping this landscape. Single analyte as well as multiplexed immunosensors applicable to point of care scenarios are presented. A section on the areas of clinical application then creates the bridge to day-to-day diagnostic practice. Finally, the depicted developments are critically weighed and future perspectives discussed in order to give the reader a firm idea on the forthcoming trends to be expected in this diagnostic field.

A Black Swan in clinical laboratory practice: the analytical error due to interferences in immunoassay methods

It is well known that the results of immunoassay methods can be affected by specific or non-specific interferences, ranging from 0.4% to 4.0%. The presence of interference may greatly compromise the accuracy of immunoassay analyses causing an error in the measurement, producing false-positive or false-negative results. From a clinical point of view, these analytical errors may have serious implications for patient care because they can cause misdiagnosis or inappropriate treatment. Unfortunately, it is a very difficult task to identify the irregular analytical errors related to immunoassay methods because they are not detectable by normal laboratory quality control procedures, are reproducible within the test system, may be clinically plausible and are relatively rare. The first line of defense against erroneous results is to use in laboratory practice only immunoassay systems with the highest level of robustness against interference. The second line of defense is always taking into account the possibility of interference in immunoassay results. A correct approach should be addressed on identification of samples at high risk of interference. The attainment of this goal requires a critical review of the test result in relation to patient's clinical conditions and literature data, taking into account the analytical characteristics of the immunoassay system. The experts in immunoassay systems should make every effort to find some specific and reliable quality indicators for irregular analytical errors in order to better detect and monitor erroneous immunoassay results due to specific or non-specific interferences.

Prevalence of interfering antibodies in dogs and cats evaluated using a species-independent assay

BACKGROUND

Interfering antibodies in human serum and plasma are known to react with mammalian antibodies in immunoassays and cause false-positive test results. Although this phenomenon was recently shown in companion animals, knowledge regarding immunoassay interference in veterinary medicine is very limited.

OBJECTIVES

The aims of this study were to set up a species-independent immunoassay procedure to detect interference in serum samples, to screen for interference in a cross-section of canine and feline patient samples from an animal hospital, and to determine if the detected interference could be neutralized using an immunoassay based on nonmammalian reagents.

METHODS

A 2-site sandwich-type interference assay was set up using commercially available mouse reagents. A total of 369 serum samples from 320 dogs and 263 samples from 218 cats were analyzed using the interference assay. Multiple samples were submitted from 36 dogs and 39 cats. Nineteen samples identified as interference-positive were analyzed in an assay using chicken antibodies.

RESULTS

Interference was detected in samples from 28 dogs (9%) and 10 cats (5%) screened with the interference assay. Except for 1 cat, consistent results were obtained for all 75 dogs and cats that submitted more than 1 sample. The interference was eliminated when analyzed in the chicken-based assay (P < .001).

CONCLUSIONS

Substances with reactivity toward mouse IgG can be detected in serum samples from dog and cat patients using a 2-site interference assay. The detected substances are most likely interfering antibodies, possibly originating from immunization with other mammalian species.

When laboratory tests can mislead even when they appear plausible

A laboratory test has three phases, pre-analytical, analytical and post-analytical. The purpose of this review is to highlight an issue concerning the analytical phase of one of the most widely deployed groups of in vitro diagnostic tests using a common technology - namely immunoassay.Immunoassay entails an inherently high error rate and, therefore, has the potential for inaccurate and misleading results susceptible to misinterpretation and/or diagnostic misapplication by clinicians. An approach based on Bayesian inference (without mathematics or equations) - illustrated by examples - is presented; this may help clinicians in discerning potentially erroneous results even when they appear plausible and not unreasonable.Essentially, false positive results are most likely to occur when the disease prevalence/incidence is low. False negative results become more prominent when the prevalence/incidence of disease increases. When concern is raised, available follow-up laboratory tests should be initiated to establish with confidence the diagnostic reliability or unreliability of such results.

The insulin autoimmune syndrome (IAS) as a cause of hypoglycaemia: an update on the pathophysiology, biochemical investigations and diagnosis

Insulin autoimmune syndrome (IAS) is considered to be very rare in Caucasians. Understanding its pathophysiology is paramount in (a) appreciating its potential impact on analyses of pancreatic hormones and (b) explaining its highly variable clinical manifestations in non-diabetic, non-acutely ill patients with indeterminate hypoglycaemia. The underlying aetiology of IAS is the presence of variable affinity/avidity endogenous insulin antibodies in significant amounts. The two types of insulin antibodies namely antibodies which bind insulin and/or proinsulin(s) and receptor antibodies (insulin mimetic) will be discussed. Their biochemical and immunological roles in causing hypoglycaemia will be highlighted. Clinical manifestations of IAS can vary from mild and transient to spontaneous, severe and protracted hypoglycaemia necessitating in extreme cases plasmapheresis for glycaemic control. Antibodies of IAS can interfere in pancreatic immunoassay tests causing erroneous and potentially misleading results. Thorough testing for endogenous insulin antibodies must be considered in the investigations of non-diabetic, non-acutely ill patients with indeterminate and/or unexplained hypoglycaemia.

Avoiding Misdiagnosis Due to Antibody Interference with Serum Free Thyroxin

INTRODUCTION

Interfering antibodies are capable of causing potentially misleading results in automated thyroid hormone immunoassays.

CASE PRESENTATION

We report the case of a 46- year-old female patient with autoimmune hypothyroidism in chronic replacement treatment with levothyroxine who was presented 8 years after diagnosis with a thyroid function test showing an increased level of TSH and a very high level of FT4. Interference in the laboratory serum free thyroxin (FT4) test was suspected, due to the lack of symptoms of hyperthyroidism and a different immunoassay platform confirmed a low FT4 result. The discrepancy between the two results was explained by the presence of antiT4-autoantibodies.

CONCLUSIONS

Antibody interference with serum free thyroxine must be considered when clinical findings and laboratory results show discrepancies.

Falsely elevated troponin: rare occurrence or future problem

Introduction

Troponins are known to be released in response to cardiac damage and therefore are the biomarkers of choice for the early diagnosis of acute myocardial infarction (AMI), improving outcome in patients presenting with chest pain. However, false results can occur due to interference from other substances in the blood.

Case

A 52-year-old male with a past medical history of alcohol abuse, hypertension, and coronary artery bypass graft at age 34 with normal stress test 2 years before presented to the emergency department (ED) complaining of 1 day of non-exertional chest pain with radiation to the neck and left arm. His troponin was elevated to 5 ng/mL in two samples drawn 12 h apart, with normal CK-MB. Renal function was normal. Electrocardiogram (ECG) showed normal sinus rhythm with no ST elevations or depressions. He underwent cardiac catheterization which showed no obstructive lesions. Five years later, he returned to the ED with abdominal pain and shortness of breath. Troponin was elevated and showed no signs of downtrend on repeat every 6 h. ECG was unchanged from 5 years before. He was discharged with a follow-up cardiac computed tomography (CT). Troponin was measured on the day of his scan and remained elevated; he was asymptomatic. Cardiac CT showed unremarkable coronaries and bypass grafts. Given persistently positive troponin in the setting of minimal to no symptoms, he was thought to have falsely elevated troponins. Centrifugation and 2:1 dilution of the sample resulted in the same general value, respectively. Rheumatoid factor and heterophile antibodies were negative. When his blood sample was sent to a different hospital utilizing a three-site immunoassay method, the value was found zero.

Discussion

Cardiac troponins (cTn) are structural proteins unique to the heart, not expressed outside of cardiac tissue and have high sensitivity and specificity for myocardial damage. Therefore, it is the test of choice for the diagnosis of AMI. When an increased troponin value is encountered in the absence of myocardial infarction, other etiologies should be explored, including vasculitis, drug abuse, myocarditis, pulmonary embolism, sepsis, and renal failure. If the clinical picture is not consistent with the elevated lab value, it is necessary to think of other causes, including false-positive results. The prevalence of this type of interference is likely to worsen in the future because of the emergence of immunotherapy in the treatment of a wide range of conditions and the use of radiolabeled antibodies in diagnosis using immunoscintigraphic procedures. Therefore, it is important to consider this as part of the differential.

Negative interference by rheumatoid factor in alpha-fetoprotein chemiluminescent microparticle immunoassay

Background Rheumatoid factor causes positive interference in multiple immunoassays. Recently, negative interference has also been found in immunoassays in the presence of rheumatoid factor. The chemiluminescent microparticle immunoassay is widely used to determine serum alpha-fetoprotein. However, it is not clear whether the presence of rheumatoid factor in the serum causes interference in the chemiluminescent microparticle immunoassay of alpha-fetoprotein. Methods Serum alpha-fetoprotein was determined using the ARCHITECT alpha-fetoprotein assay. The estimation of alpha-fetoprotein recovery was carried out in samples prepared by diluting high-concentration alpha-fetoprotein serum with rheumatoid factor-positive or rheumatoid factor-negative serum. Paramagnetic microparticles coated with hepatitis B surface antigen-anti-HBs complexes were used to remove rheumatoid factor from the serum. Results The average recovery of alpha-fetoprotein was 88.4% and 93.8% in the rheumatoid factor-positive and rheumatoid factor-negative serum samples, respectively. The recovery of alpha-fetoprotein was significantly lower in the rheumatoid factor-positive serum samples than in the rheumatoid factor-negative serum samples. In two of five rheumatoid factor-positive samples, a large difference was found (9.8%) between the average alpha-fetoprotein recoveries in the serially diluted and initial recoveries. Fourteen rheumatoid factor-positive serum samples were pretreated with hepatitis B surface antigen-anti-HBs complex-coated paramagnetic microparticles. The alpha-fetoprotein concentrations measured in the pretreated samples increased significantly. Conclusions It was concluded that the alpha-fetoprotein chemiluminescent microparticle immunoassay is susceptible to interference by rheumatoid factor, leading to significantly lower results. Eliminating the incidence of negative interference from rheumatoid factor should be an important goal for immunoassay providers. In the meantime, laboratorians must remain alert to the negative interference by rheumatoid factor, and in some cases, pretreat rheumatoid factor-positive samples with blocking or absorbing reagents.

FDA-approved drugs that interfere with laboratory tests: A systematic search of US drug labels

Drug-related laboratory test interference or drug/laboratory test interactions (DLTI) are a major source of laboratory errors. DLTI is of concern with regard to both the clinical diagnosis and the monitoring of patients. Although there have been numerous reports about specific drugs that interfere with laboratory tests, there has not been a recent review on the topic. We herein provide a review of the known DLTI of US FDA-approved drugs based on a systematic search of DailyMed, a website containing the labels of US FDA-approved drugs. The labels for all human single-ingredient prescription drugs included in the database (1368) were searched using stemmed keywords and were manually reviewed for their relevance to DLTI. A total of 134 labels were positive, which indicated that the drug interferes with at least one clinical laboratory test. Antibacterial agents, psychotropic drugs and contrast media are the classes of drugs most likely to lead to DLTI. Urine was the clinical sample most frequently affected by DLTI. The FDA drug label is a source of information for studies of DLTI, although information is still lacking for most drugs, and additional improvements are needed for many of the existing records. Medical professionals, clinicians and laboratory staff should keep these possible interactions in mind when interpreting the results of laboratory tests, and should ensure that they obtain a complete and accurate record of all drugs being used by patients in order to anticipate potential DLTI. The development of a reporting system to address potential DLTI is warranted.

Achievement of linear response for competitive bioaffinity assays of ligands: criteria of optimized interaction systems

For a linear response, an optimized competitive bioaffinity assay of a ligand requiresC_RT> 3 ×C_PT,C_PT> 50 ×K_dR, andK_dR> 260 ×K_dX(C_RTandC_PTare concentrations of the probe and protein whileK_dXandK_dRareK_dfor the ligand and probe, respectively).

Pseudohyperthyroxinemia in a hypothyroid patient secondary to chronic phlegmon

Background: Elevated free thyroxine could be primary or secondary, endogenous or exogenous and often presents with symptoms of hyperthyroidism. Thyroxine levels are low in hypothyroidism, where the individual requires exogenous supplementation to maintain a euthyroid state. However, thyroxine levels may be elevated in a hypothyroid patient because of over-supplementation/over-suppression with exogenous agent(s) or secondary to other pathologies and rarely, laboratory error or assay interference may cause alteration in the levels of the thyroid hormones.

Case report: A 44-year-old man with well controlled hypothyroidism was referred for assessment of markedly elevated TSH and free thyroxine levels with low free T3. Clinically the patient was hypothyroid with symptoms of fatigue and weight gain of 30 pounds over the past 3-months and the TSH levels were consistent with marked hypothyroidism. However, free thyrxoine was markedly elevated, opposite of what to be expected. A systematic evaluation, presented here, was helpful in the diagnosis of pseudohyperthyroxinemia secondary to assay interferences in a timely fashion, avoiding unnecessary further investigations.

Conclusions: Interference in immunoassays is an important clinical problem that is underestimated and can have important clinical consequences. It is important to recognize the possibility of such interferences early in the diagnostic process and to implement protocols to identify these whenever possible, in a timely fashion, to prevent untoward consequences. Vigilance by both the clinician and the laboratory staff is important.

Up-to-Date Applications of Microarrays and Their Way to Commercialization

This review addresses up-to-date applications of Protein Microarrays. Protein Microarrays play a significant role in basic research as well as in clinical applications and are applicable in a lot of fields, e.g., DNA, proteins and small molecules. Additionally they are on the way to enter clinics in routine diagnostics. Protein Microarrays can be powerful tools to improve healthcare. An overview of basic characteristics to mediate essential knowledge of this technique is given. To reach this goal, some challenges still have to be addressed. A few applications of Protein Microarrays in a medical context are shown. Finally, an outlook, where the potential of Protein Microarrays is depicted and speculations how the future of Protein Microarrays will look like are made.