Unusual results from immunoassays and the role of the clinical endocrinologist

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.

Interference by macroprolactin in assays for prolactin: will the In Vitro Diagnostics Regulation lead to a solution at last?

Cross reactivity with high molecular weight complexes of prolactin known as macroprolactin is a common cause of positive interference in assays for serum prolactin. All prolactin assays currently available are affected with 5-25% of results indicating hyperprolactinaemia falsely elevated due to macroprolactinaemia - hyperprolactinaemia due to macroprolactin with normal concentrations of bioactive monomeric prolactin. Macroprolactinaemia has no pathological significance but, if it is not recognised as the cause, the apparent hyperprolactinaemia can lead to clinical confusion, unnecessary further investigations, inappropriate treatment and waste of healthcare resources. Macroprolactinaemia cannot be distinguished from true hyperprolactinaemia on clinical grounds alone but can be detected by a simple laboratory test based on the precipitation of macroprolactin with polyethylene glycol. Laboratory screening of all cases of hyperprolactinaemia to exclude macroprolactinaemia has been advised as best practice but has not been implemented universally and reports of clinical confusion caused by macroprolactinaemia continue to appear in the literature. Information provided by manufacturers to users of assays for prolactin regarding interference by macroprolactin is absent or inadequate and does not comply with the European Union Regulation covering in vitro diagnostic medical devices (IVDR). As the IVDR is implemented notified bodies should insist that manufacturers of assays for serum prolactin comply with the regulations by informing users that macroprolactin is a source of interference which may have untoward clinical consequences and by providing an estimate of the magnitude of the interference and a means of detecting macroprolactinaemia. Laboratories should institute a policy for excluding macroprolactinaemia in all cases of hyperprolactinaemia.

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.

The simultaneous quantitative detection of multiple hormones based on PS-MS: affinity capture by a single antibody

Here, we utilized single antibody to capture and separate multiple hormones from samples to avoid LC procedures and MS/MS detection to realize simultaneously qualitative and quantitative analysis of multiple molecules in a single run.

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.

Influence of exogenous and endogenous factors on the quality of the preanalytical stage of laboratory tests (review of literature)

A literature review in the article presents an analysis of the influence of endogenous and exogenous factors on quality of preanalytical phase of laboratory testing. The review shows significance of external and internal factors influencing blood samples at preanalytical phase of laboratory testing. Among the exogenous factors considered: phlebotomy, test tubes for samples, transportation and storage. A number of factors exist at this phase that significantly affect test results. We examined these aspects of phlebotomy process: staff training, disinfectant contamination, needle diameter, needle material contamination. The review considers possible contamination with tube components and the importance of choosing the right anticoagulants and excipients. Transportation and storage of biological samples can be a source of errors at the preanalytical phase of laboratory testing. We analyzed the problem of determining the stability of analytes during storage and aspects of transportation samples by modern means. Among the endogenous factors considered: hemolysis, lipemia, icterricity, cell metabolism.. Hemolysis is one of the most frequent consequences of errors at the preanalytical phase. We analyzed importance of choosing a method for identifying hemolized tubes and the heterogeneity of bias results on different analytical systems. The review shows contribution of various classes of lipoproteins to turbidity of sample, possible preanalytical errors and impact on analytical tests. We examined possible effects of high bilirubin concentrations on analyte measurements. In the review, we also examined metabolism of some cells and its effect on samples.

ADRENOCORTICOTROPIC HORMONE IMMUNOASSAY INTERFERENCE IN A PATIENT WITH SUBCLINICAL HYPERCORTISOLISM

Context

Immunoassays are vulnerable to occasional analytical errors despite their sensitivity and specificity. Adrenocorticotropic hormone (ACTH) is among hormones which are vulnerable to assay interference.

Objective

In this case report, we aimed to present a case of ACTH interference in a patient with subclinical hypercortisolism.

Case report

We present a case of subclinical hypercortisolism with unexpectedly elevated levels of ACTH in whom interference was shown by different biochemical methods.It is important for the clinician to keep in mind the possibility of interference when clinical and laboratory results are discordant. The communication between the clinician and laboratory staff is important while interpreting results. This case report shows that ACTH interference should be considered in patients with subclinical hypercortisolism who have unexpectedly high levels of adrenocorticotropic hormone.

Harnessing the potential of blood donation archives for influenza surveillance and control

Many blood donation services around the globe maintain large archives of serum and/or plasma specimens of blood donations which could potentially be used for serologic surveillance and risk assessment of influenza. Harnessing this potential requires robust evidence that the outcomes of influenza serology in plasma, which is rarely used, is consistent with that in serum, which is the conventional choice of specimens for influenza serology. We harvested EDTA-plasma specimens from the blood donation archives of Hong Kong Red Cross Transfusion Services, where EDTA is the type of anticoagulant used for plasma collection, compared their antibody titers and responses to that in serum. Influenza A/H1N1/California/7/2009 and A/H3N2/Victoria/208/2009 were the test strains. Our results showed that antibody titers in 609 matched serum/EDTA-plasma specimens (i.e. obtained from the same donor at the same time) had good agreement inferred by Intraclass Correlation Coefficient, the value of which was 0.82 (95% CI: 0.77-0.86) for hemagglutination inhibition assay and 0.95 (95% CI: 0.93-0.96) for microneutralization assay; seroconversion rates (based on hemagglutination inhibition titers) during the 2010 and 2011 influenza seasons in Hong Kong inferred from paired EDTA-plasma were similar to that inferred from paired sera. Our study provided the proof-of-concept that blood donation archives could be leveraged as a valuable source of longitudinal blood specimens for the surveillance, control and risk assessment of both pandemic and seasonal influenza.

Irregular analytical errors in diagnostic testing - a novel concept

BACKGROUND

In laboratory medicine, routine periodic analyses for internal and external quality control measurements interpreted by statistical methods are mandatory for batch clearance. Data analysis of these process-oriented measurements allows for insight into random analytical variation and systematic calibration bias over time. However, in such a setting, any individual sample is not under individual quality control. The quality control measurements act only at the batch level. Quantitative or qualitative data derived for many effects and interferences associated with an individual diagnostic sample can compromise any analyte. It is obvious that a process for a quality-control-sample-based approach of quality assurance is not sensitive to such errors.

CONTENT

To address the potential causes and nature of such analytical interference in individual samples more systematically, we suggest the introduction of a new term called the irregular (individual) analytical error. Practically, this term can be applied in any analytical assay that is traceable to a reference measurement system. For an individual sample an irregular analytical error is defined as an inaccuracy (which is the deviation from a reference measurement procedure result) of a test result that is so high it cannot be explained by measurement uncertainty of the utilized routine assay operating within the accepted limitations of the associated process quality control measurements.

SUMMARY

The deviation can be defined as the linear combination of the process measurement uncertainty and the method bias for the reference measurement system. Such errors should be coined irregular analytical errors of the individual sample. The measurement result is compromised either by an irregular effect associated with the individual composition (matrix) of the sample or an individual single sample associated processing error in the analytical process.

OUTLOOK

Currently, the availability of reference measurement procedures is still highly limited, but LC-isotope-dilution mass spectrometry methods are increasingly used for pre-market validation of routine diagnostic assays (these tests also involve substantial sets of clinical validation samples). Based on this definition/terminology, we list recognized causes of irregular analytical error as a risk catalog for clinical chemistry in this article. These issues include reproducible individual analytical errors (e.g. caused by anti-reagent antibodies) and non-reproducible, sporadic errors (e.g. errors due to incorrect pipetting volume due to air bubbles in a sample), which can both lead to inaccurate results and risks for patients.

Influence of sample collection tube method, anticoagulant-containing plasma versus serum, on influenza virus hemagglutination inhibition titer and microneutralization titer serological assays

BACKGROUND

The hemagglutination-inhibition (HAI) assay is a critical component for measurement of immunogenicity in influenza vaccine development. It is unknown if the results can be influenced by sample type and anticoagulants. The purpose of this study was to evaluate the influence of different sample collection methods, in particular different anticoagulants, and choice of plasma or serum, on influenza virus serological assays.

METHODS

Blood samples from thirty donors previously immunized against influenza viruses were collected using six different types of blood collection tubes, two of which collect serum and four of which contain various anticoagulants for collecting plasma. Serum: (1) serum separator tubes (SST); and (2) Plus Plastic serum "red-top serum" tubes. Plasma: (3) spray-coated K2 ethylenediaminetetraacetic acid (EDTA) tubes: (4) Sodium Heparin tubes; (5) Citrate tubes with 3.2% sodium citrate solution; and (6) Glass Blood Collection tubes with acid citrate dextrose. Samples were tested against three different influenza viruses (A/California/07/2009 (H1N1pdm09), A/Texas/50/2012 (H3N2), and B/Massachusetts/2/2012) for hemagglutination inhibition titer and virus neutralization titer via a microneutralization (MN) assay, and data compared to that obtained for standard serum sample collected in SST.

RESULTS

HAI and MN titers against type A viruses were within two dilutions compared to SST collection method over 96% of the time irrespective of sample type or anticoagulant. However, HAI titers for type B virus were more variable across different collection methods. EDTA plasma samples were greater than two dilutions higher than SST serum samples 70% (21 of 30 samples) of the time. In contrast, MN titers were within two dilutions over 96% of the time, with the highest deviation noted in acid citrate dextrose plasma samples (3 of 30 samples tested, 10%).

CONCLUSIONS

These data provide useful guidelines for sample collection and serology testing when screening: (i) influenza vaccine immunogenicity antibody response; (ii) antibody responses to newly emerging viral strains; and (iii) clinical samples for anti-influenza antibody activity.

Accuracy of Two Progesterone Immunoassays for Monitoring In Vitro Fertilization

BACKGROUND

Progesterone concentrations are routinely monitored during in vitro fertilization cycles. Immunoassay-based platforms are used most often in this setting because they are simple to use and amenable to same-day sample collection and result-reporting. However, immunoassay methods are subject to variation in specificity between different assay manufacturers. In this study, a set of unexpectedly high progesterone concentrations led to a method comparison between two in-house immunoassay platforms relative to the reference method.

METHODS

Progesterone was measured in 28 serum samples from women undergoing IVF cycles using the Siemens ADVIA Centaur Immunoassay system and the Abbott Architect i1000SR analyzer. A subset of these samples was selected for progesterone measurement by liquid chromatography-tandem mass spectrometry to define the accuracy of each immunoassay.

RESULTS

The Siemens ADVIA Centaur immunoassay system overestimated progesterone concentrations by 19% and the Abbott Architect overestimated progesterone concentrations by 5%.

CONCLUSIONS

The Abbott Architect progesterone immunoassay provides a more accurate measurement of serum progesterone than the Centaur immunoassay at concentrations relevant for monitoring in vitro fertilization populations.

Interference in ACTH immunoassay negatively impacts the management of subclinical hypercortisolism

PURPOSE

Low plasma corticotropin is considered a useful parameter for the diagnosis of subclinical hypercortisolism in patients with an adrenal incidentaloma. However, immunoassays are vulnerable to interference from endogenous antibodies. In this study, subjects who underwent Hypothalamus-pituitary-adrenal axis evaluation for the assessment of subclinical hypercortisolism were evaluated. The objective of the study was to ascertain whether antibody interference in corticotropin immunoassay affected the diagnostic work-up and clinical decisions.

METHODS

The 437 consecutive patients with incidentally discovered adrenal adenomas were included in this single centre study. Patients who had a combination of a nonsuppressed corticotropin concentration (>4.4 pmol/L) and a non-suppressed cortisol concentration after 1 mg overnight dexamethasone suppression test (>50 nmol/L) were selected. Eight eligible subjects without specific features of Cushing's syndrome were identified and recruited for interference studies and follow-up. Nine controls including one patient with unilateral adrenalectomy and one patient with Cushing's disease were recruited as well.

MEASUREMENTS

Eligible subjects and controls were subjected to hormonal tests and investigations for suspected interference. Interference studies included measurement of corticotropin on a different analytical platform, serial dilutions, polyethylene glycol precipitation and heterophilic antibody analysis. Patients were followed with clinical and laboratory parameters for a median duration of 30 (12-90) months.

RESULTS

Antibody interference was identified in four patients. Rheumatoid factor was responsible for the interference in one patient. Clinical management of the patients was affected by the erroneous results. Interference tests were negative in control subjects.

CONCLUSIONS

Erroneous results associated with analytical interference negatively impacted on clinical decision making in this patient group. This should be considered particularly in conditions such as subclinical hypercortisolism which decisions depend on laboratory investigations mainly. Analytical interference could explain the high variability observed both in field measurements from patients who were expected to have lower corticotropin concentrations and in subclinical hypercortisolism prevalence reported by different studies. Many problems can be resolved by ensuring good communication between clinical and laboratory staff.

Diagnostic Dilemma in Discordant Thyroid Function Tests Due to Thyroid Hormone Autoantibodies

OBJECTIVE

Assay interference could be the cause of abnormal thyroid function tests. Early recognition prevents inappropriate patient management. The objective of this report is to present a case with discordant thyroid function tests in different thyroid assay platforms due to thyroid autoantibodies.

METHODS

We present a case her family, laboratory data and methods that investigate immunoassay interference.

RESULTS

A 21-year-old woman with autoimmune thyroid disease was treated for hypothyroidism with levothyroxine and noted to have elevated total and free thyroxine, free triiodothyronine but normal thyroid-stimulating hormone. Repeat thyroid function tests using different platforms revealed discrepant results. Further investigation showed that the patient had positive thyroid hormone autoantibodies (THAAbs).

CONCLUSION

We demonstrates abnormal thyroid function tests caused by THAAbs. The latter were the cause of interference with assays resulting in discrepant test results inconsistent with the clinical presentation. Early recognition would prevent inappropriate patient management.

Exogenous sample contamination. Sources and interference

Clinical laboratory medicine is involved in the vast majority of patient care pathways. It has been estimated that pathology results inform 60-70% of critical patient care decisions. The primary goal of the laboratory is to produce precise and accurate results which reflect the true situation in vivo. It is not surprising that interference occurs in laboratory analysis given the complexity of some of the assays used to perform them. Interference is defined as "the effect of a substance upon any step in the determination of the concentration or catalytic activity of the metabolite". Exogenous interferences are defined as those that derive from outside of the body and are therefore not normally found in a specimen and can cause either a positive or negative bias in analytical results. Interferences in analysis can come from various sources and can be classified as endogenous or exogenous. Exogenous substances could be introduced at any point in the sample journey. The laboratory must take responsibility for the quality of results produced. It has a responsibility to have processes in place to identify and minimise the occurrence and effect contamination and interference. To do this well the laboratory needs to work with clinicians and manufacturers. Failure to identify an erroneous result could have an impact on patient care, patient safety and also on hospital budgets. However it is not always easy to recognise interferences. This review summarises the types and sources of exogenous interference and some steps to minimise the impact they have.

The degree of acceptability of swine blood values at increasing levels of hemolysis evaluated through visual inspection versus automated quantification

The pronounced fragility that characterizes swine erythrocytes is likely to produce a variable degree of hemolysis during blood sampling, and the free hemoglobin may then unpredictably bias the quantification of several analytes. The aim of this study was to evaluate the degree of acceptability of values obtained for several biochemical parameters at different levels of hemolysis. Progressively increased degrees of physical hemolysis were induced in 3 aliquots of 30 nonhemolytic sera, and the relative effects on the test results were assessed. To define the level of hemolysis, we used both visual estimation (on a scale of 0 to 3+) and analytical assessment (hemolytic index) and identified the best analytical cutoff values for discriminating the visual levels of hemolysis. Hemolysis led to a variable and dose-dependent effect on the test results that was specific for each analyte tested. In mildly hemolyzed specimens, C-reactive protein, haptoglobin, β1-globulin, β2-globulin, α1-globulin, γ-globulin, sodium, calcium, and alkaline phosphatase were not significantly biased, whereas α2-globulin, albumin, urea, creatinine, glucose, total cholesterol, aspartate aminotransferase, alanine aminotransferase, gamma-glutamyl transferase, nonesterified fatty acids, bilirubin, phosphorus, magnesium, iron, zinc, copper, lipase, triglycerides, lactate dehydrogenase, unbound iron-binding capacity, and uric acid were significantly biased. Chloride and total protein were unbiased even in markedly hemolyzed samples. Analytical interference was hypothesized to be the main source of this bias, leading to a nonlinear trend that confirmed the difficulty in establishing reliable coefficients of correction for adjusting the test results.

Serum sample containing endogenous antibodies interfering with multiple hormone immunoassays. Laboratory strategies to detect interference

OBJECTIVES

Endogenous antibodies (EA) may interfere with immunoassays, causing erroneous results for hormone analyses. As (in most cases) this interference arises from the assay format and most immunoassays, even from different manufacturers, are constructed in a similar way, it is possible for a single type of EA to interfere with different immunoassays. Here we describe the case of a patient whose serum sample contains EA that interfere several hormones tests. We also discuss the strategies deployed to detect interference.

SUBJECTS AND METHODS

Over a period of four years, a 30-year-old man was subjected to a plethora of laboratory and imaging diagnostic procedures as a consequence of elevated hormone results, mainly of pituitary origin, which did not correlate with the overall clinical picture.

RESULTS

Once analytical interference was suspected, the best laboratory approaches to investigate it were sample reanalysis on an alternative platform and sample incubation with antibody blocking tubes. Construction of an in-house 'nonsense' sandwich assay was also a valuable strategy to confirm interference. In contrast, serial sample dilutions were of no value in our case, while polyethylene glycol (PEG) precipitation gave inconclusive results, probably due to the use of inappropriate PEG concentrations for several of the tests assayed.

CONCLUSIONS

Clinicians and laboratorians must be aware of the drawbacks of immunometric assays, and alert to the possibility of EA interference when results do not fit the clinical pattern.

A possible analytical and clinical role of endogenous antibodies causing discrepant adrenocorticotropic hormone measurement in a case of ectopic Cushing’s syndrome

Heterophilic antibodies are well described, but poorly appreciated interferents and is often not a recognized problem affecting most immunoassays. We report a patient presented with ectopic Cushing’s syndrome (CS), but repeated plasma adrenocorticotropic hormone (ACTH) concentrations conducted by immunoassay were inappropriately within the reference range and not elevated, most probably as a result of antibody interference. A 36-year-old woman, presented with large gastric neuroendocrine carcinoma and severe ectopic CS, while repeated plasma ACTH concentrations conducted by immunoassay were inappropriately within the reference range. As we expected ACTH concentration to be higher, we performed several tests to evaluate whether there was any assay interference causing falsely lower than expected ACTH results. We measured ACTH using a different immunoassay, assayed the sample in dilution, assayed the sample after being incubated in heterophilic antibody blocking agent tube and performed recovery studies. Tests indicated the presence of interfering compounds, most probably heterophilic antibodies. When clinicians find ACTH concentrations to be lower than expected, we recommend the laboratory investigate antibody interference.

Dysthyronemia in normal concentrations of thyrotropin--analytical and clinical consequences

This article discusses the conditions that may lead to a phenomenon called dysthyronemia. Here, the thyroid gland has concentration of thyrotropin in circulation within the reference range, but the concentrations of free or total fractions of thyroid hormones are outside the reference range. Normal values of thyrotropin (TSH) and increased values of THs are referred to as hyperthyroxinemia, while normal values of thyrotropin and decreased values of thyroid hormone are hypothyroxinemia. As shown by our observations, it is a relatively frequent situation in the parallel determinations of TSH and free thyroxine, when results verging on hyperthyroxinemia were found in 7% of cases (6.74%, n=259,590), and also in the parallel sets of TSH and total triiodothyronine when hypotriiodothyroninemia reached 8.5% (8.48%, n=73,143). We are assuming that the main cause of hyperthyroxinemia in the free thyroxine and TSH system is the presence of autoantibodies against thyroxine in patients with autoimmune thyroid disease. The reason of hypotriiodothyroninemia in the system of triiodothyronine and TSH is a decreased concentration of thyroid binding globulin in postmenopausal women. Manufacturers of immunoanalytical kits should take into account the potential adverse effects of autoantibodies against thyroid hormones when measuring the results of immunoassay determination of the free fraction of these hormones.

Comparative analysis of hemagglutination inhibition titers generated using temporally matched serum and plasma samples

Influenza-specific hemaggluitination inhibition (HAI) antibody titer, an indicator of immunity to influenza, is often used to measure exposure to influenza in surveillance and immunogenicity studies. Traditionally, serum has been the specimen of choice for HAI assays, but a desire to reduce the amount of blood collected during studies and the availability of plasma in archived sample collections warrant the evaluation of plasma for HAI titer. Therefore, the relationship between serum and plasma HAI titer values is of great interest. Here, we compare HAI titers determined on temporally matched serum and plasma (citrated and heparinized) using influenza A and B viruses. Bland-Altman plots, McNemar's test, and geometric coefficient of variation were used respectively for evaluating agreement, correlation and variability in the serum-plasma titer results. We observed a high degree of agreement (80.5%–98.8%) and correlation (r = 0.796–0.964) in the serum and matched plasma titer values although plasma titers were generally lower than corresponding serum titers. Calculated seropositive (HAI ≥40) rates were higher using serum titers than with plasma titers, but seroconversion rates were unaffected by sample type. Stronger agreement and decreased variability in titers were seen between serum and citrated plasma than between serum and heparinized plasma. Overall, these data suggest that serum or plasma can be used in serodiagnostic HAI assays, but seropositive rates may be underestimated using plasma HAI titers. The type of anticoagulant present in plasma may affect HAI titer values and warrants further investigation.

Characterization of anti-natalizumab antibodies in multiple sclerosis patients

BACKGROUND

A small proportion of multiple sclerosis (MS) patients treated with natalizumab develop anti-drug antibodies.

OBJECTIVE

The objective of this paper is to characterize the anti-natalizumab antibody response and to investigate differences between persistently and transiently antibody-positive patients.

METHODS

Screening for anti-natalizumab antibodies was performed using a standardized bridging ELISA. Antibody-positive samples were further analyzed for IgM and IgG1-4 antibodies using ELISA and ImmunoCAP®.

RESULTS

Anti-natalizumab antibodies developed in 57 of 1379 (4.1%) treated patients after a median treatment duration of three months. Of the positive patients, 20 (35%) patients reverted to negative, 19 (33%) patients were confirmed persistently positive and 18 (32%) patients were unconfirmed positive. Significantly higher anti-natalizumab antibody levels were detected in persistently compared to transiently positive patients. A cutoff value predicting persistence of antibodies could be determined with a sensitivity of 0.84 and a specificity of 0.80. IgM and IgG4 antibody levels were significantly higher in persistently compared to transiently positive patients, and IgG1, IgG2 and IgG4 increased significantly over time.

CONCLUSIONS

The level of total anti-natalizumab antibodies in a first positive sample can be used to predict patients at risk for persisting antibody positivity. However, neither IgM nor IgG1-4 antibodies could be used to discriminate between transiently and persistently positive patients.

Intermittent and recurrent episodes of subclinical hypothyroidism, central hypothyroidism and T3-toxicosis in an elderly woman

Exogenous thyrotoxicosis is usually caused by ingestion of excessive amounts of thyroid hormone, which could be intentional or surreptitious (known as factitious thyrotoxicosis). Non-pharmacological exogenous thyrotoxicosis is an exceptional event. One example is alimentary thyrotoxicosis, which is caused by the ingestion of meat or sausage containing thyroid tissue, inadvertently mixed with traces of muscles and other tissues of the animal's neck (hamburger thyrotoxicosis). We report for the first time a patient who had recurrent episodes of triiodothyronine (T3) toxicosis for several years due to inadvertent chronic consumption of contaminated traditional Spanish cold meat with porcine thyroid.

Interpretation of hormone levels in older patients: points for consideration

Blood hormone and tumor marker concentrations are usually determined by immunochemical methods which are based on an unique reaction between antigen and assay capture antibody. Despite the speed and simplicity of assays performance on automatic immunochemistry platforms, the interpretation of final results requires a deep knowledge of method fallibility. General lack of immunoassays standardization, presence of cross-reacting substances in patient's sample, limitation of free hormones measurement due to abnormal analyte binding protein concentrations, assay interferences due to patient's autoantibodies, and heterophilic antibodies, as well as proper interpretation of very low- and very high-sample analyte levels, are the main points discussed in respect to hormones and tumor markers measurement in geriatric population.

Insights in regulated bioanalysis of human insulin and insulin analogs by immunoanalytical methods

Despite the long and illustrious history of insulin and insulin analogs as important biotherapeutics, the regulated bioanalysis (in this article, regulated bioanalysis refers to the formalized process for generating bioanalytical data to support pharmacokinetic and toxicokinetic assessments intended for development of insulin and insulin analogs as biotherapeutics, as opposed to the analytical process used for measuring insulin as a biomarker) of these peptides remains a challenging endeavor for a number of reasons. Paramount is the fact that the therapeutic concentrations are often low in serum/plasma and not too dissimilar from the endogenous level, particularly in patients with insulin resistance, such as Type 2 diabetes mellitus. Accordingly, this perspective was written to provide helpful background information for the design and conduct of immunoassays to support regulated bioanalysis of insulin and insulin analogs. Specifically, it highlights the technical challenges for determination of insulin and insulin analogs by immunoanalytical methods that are intended to support evaluations of pharmacokinetics and toxicokinetics. In a broader sense, this perspective describes the general bioanalytical issues that are common to regulated bioanalysis of peptides and articulates some of the bioanalytical differences between conventional monoclonal antibodies and peptide therapeutics.

Impact of matrix-associated soluble factors on the specificity of the immunogenicity assessment

BACKGROUND

Specificity and sensitivity are essential in assays for immunogenicity assessment of biotherapeutics. Nonspecific interactions from excess therapeutic or anti-therapeutic antibody, soluble ligands (e.g., target receptor), or serum proteins associated with autoimmune conditions (e.g., rheumatoid factor) in samples can impact the detection of a true anti-therapeutic response.

RESULTS

Electrochemiluminescence-based bridging assay formats could eliminate the interference due to rheumatoid factor with no pretreatment with Melon Gel™ or aggregated IgG. The interference due to soluble factors was not platform specific for the four therapeutics evaluated in this study.

CONCLUSION

Melon Gel pretreatment and avidin high-bind (Meso Scale Discovery) plates can effectively reduce interference due to rheumatoid factor in ELISA- and electrochemiluminescence-based assays, respectively. Excess levels of therapeutic and anti-therapeutic antibodies in bridging assays can impact assay specificity.

Evaluation of dysthyronemia in endocrinological patients

Dysthyronemia is the state of the thyroid gland in which the concentration of thyrotropin (TSH) in circulation is within the reference range, but the concentrations of free or total fractions of thyroid hormones (TH) are outside the reference range. Normal values of TSH and increased values of TH are referred to as hyperthyroxinemia or hypertriiodothyroninemia, while normal values of TSH and decreased values of TH are called hypothyroxinemia or hypotriiodothyroninemia.

Thyroid diagnostic tests were carried out at the Institute of Endocrinology, Prague, Czech Republic, in 1999–2009 using the immunoanalytical systems of Roche Diagnostics GmbH, Germany (Elecsys 2010, Modular E170).

Hyperthyroxinemia was found in 6.74% of all parallel sets of TSH and free thyroxine (FT4, n=259,590) values. Hypotriiodothyroninemia was observed in 8.48% of all parallel sets of TSH and total triiodothyronine (TT3, n=73,143). The occurrence of hyperthyroxinemia (TSH-FT4) and hypotriiodothyroninemia (TSH-TT3) was >3 times higher than the occurrence of dysthyronemia for the combinations TSH-FT4 (hypothyroxinemia), TSH-TT4 (total thyroxine, n=1996), TSH-FT3 (free triiodothyronine, n=94,090), and TSH-TT3 (hypertrijodthyroninemia), and >5 times higher in comparison with the combinations TSH-FT4-FT3 (n=93,683), TSH-FT4-TT3 (n=72,373), TSH-FT3-TT3 (n=2466), TSH-TT4-TT3 (n=1779), TSH-FT4-TT4 (n=1571), and TSH-FT3-TT4 (n=1466).

In light of our patient types, we are assuming that the observed hypotriiodothyroninemia (TSH-TT3, 8.48%) is due to a decreased concentration of thyroid binding globulin in postmenopausal women and that hyperthyroxinemia (TSH-FT4, 6.74%) is caused mainly by endogenous autoantibodies against thyroxine in patients with thyroid autoimmune diseases.

Spironolactone interference in the immunoassay of androstenedione

Background

In an evaluation of androstenedione results from patient serum samples using the Siemens Immulite 2500 analyser and manual Coat-A-Count (CAC) methods, three outliers were evident with grossly elevated results in the CAC assay.

Methods

The clinic notes of three patients with apparently high serum androstenedione concentrations by the CAC assay were checked for medications. The samples were all from patients with polycystic ovary syndrome taking 100–200 mg/d of a steroidal antiandrogen (spironolactone). Two other patients on 50 mg spironolactone per day had less markedly higher androstendione results with the CAC assay. In a further five patients who were selected since they were on spironolactone and had high androstenedione results by the CAC method, spironolactone was temporarily withdrawn and fresh blood samples obtained for analysis.

Results

Spironolactone treatment was associated with higher androstenedione concentrations measured by the CAC assay that reverted to normal on treatment withdrawal. Based on a single test with spironolactone at 1000 ng/mL, the manufacturer reported only 0.109% interference in the CAC assay.

Conclusions

Spironolactone (and/or its metabolites) may interfere in the Siemens CAC assay for androstenedione but not in the Immulite 2500 assay. This experience highlights the need for information from clinicians on drug treatment when laboratory investigations are requested. Drug interferences in immunoassay are common and need evaluation beyond tests performed to certify laboratory reagents.

Immunoglobulin interference in serum follicle-stimulating hormone assays: autoimmune and heterophilic antibody interference

Interference in immunoassay caused by endogenous immunoglobulin is a cause of incorrect laboratory results that can drastically affect patient management. Two cases of immunoglobulin interference in serum follicle-stimulating hormone (FSH) assays are presented. These cases illustrate two common mechanisms for false-positive interference in two-site (sandwich) immunoassays. The first case describes a circulating autoimmune FSH immunoglobulin complex ('macro'-FSH), which has not been previously described for FSH, and the second a cross-linking antibody directed against the assay reagents. Immunoglobulin interference was detected and characterized using a combination of method comparison, immunosubtraction and size exclusion chromatography.

Effect of exogenous circulating anti-bPL antibodies on bovine placental lactogen measurements in foetal samples

Background

The involvement of placental lactogen (PL) in the regulation of foetal growth has been investigated in different species by in vivo immunomodulation techniques. However, when circulating antibodies are present together with the hormone, the procedure for hormonal measurement becomes considerably complex. The aim of this study was the immunoneutralization of bovine placental lactogen (bPL) concentrations in bovine foetal circulation by direct infusion of rabbit anti-bPL purified immunoglobulins (IgG) via a foetal catheter (in vivo study). The ability of a RIA based on guinea pig anti-bPL antiserum, for the measurement of bPL concentrations in samples containing exogenous rabbit anti-bPL immunoglobulins, was also analyzed in in vitro and in vivo conditions.

Methods

Six bovine foetuses were chronic cannulated on the aorta via the medial tarsal artery. Infusion of rabbit anti-bPL IgG was performed during late gestation. Pooled rabbit anti-bPL antisera had a maximal neutralization capacity of 25 μg bPL/mL of immunoglobulin. Interference of rabbit anti-bPL immunoglobulin with radioimmunoassay measurement using guinea pig anti-bPL as primary antibody was first evaluated in vitro. Polyclonal anti-bPL antibodies raised in rabbit were added in foetal sera to produce 100 samples with known antibodies titers (dilutions ranging from 1:2,500 till 1:1,280,000).

Result(s)

Assessment of the interference of rabbit anti-bPL antibody showed that bPL concentrations were significantly lower (P < 0.05) in samples added with dilutions of rabbit antiserum lower than 1:80,000 (one foetus) or 1:10,000 (four foetuses). It was also shown that the recovery of added bPL (12 ng/mL) was markedly reduced in those samples in which exogenous rabbit anti-bPL were added at dilutions lower than 1:20,000. Concentrations of foetal bPL were determined in samples from cannulated foetuses. In foetuses 1 and 6, bPL concentrations remained almost unchanged (<5 ng/mL) during the whole experimental period. In Foetus 3, bPL concentrations decreased immediately after IgG infusion and thereafter, they increased until parturition.

Conclusion(s)

The use of a bPL RIA using a guinea pig anti-bPL as primary antiserum allowed for the measurement of bPL concentrations in foetal plasma in presence of rabbit anti-bPL IgG into the foetal circulation. Long-term foetal catheterization allowed for the study of the influence of direct infusion of anti-bPL IgG on peripheral bPL concentrations in bovine foetuses.

Impact of blood collection devices on clinical chemistry assays

Blood collection devices interact with blood to alter blood composition, serum, or plasma fractions and in some cases adversely affect laboratory tests. Vascular access devices may release coating substances and exert shear forces that lyse cells. Blood-dissolving tube additives can affect blood constituent stability and analytical systems. Blood tube stoppers, stopper lubricants, tube walls, surfactants, clot activators, and separator gels may add materials, adsorb blood components, or interact with protein and cellular components. Thus, collection devices can be a major source of preanalytical error in laboratory testing. Device manufacturers, laboratory test vendors, and clinical laboratory personnel must understand these interactions as potential sources of error during preanalytical laboratory testing. Although the effects of endogenous blood substances have received attention, the effects of exogenous substances on assay results have not been well described. This review will identify sources of exogenous substances in blood specimens and propose methods to minimize their impact on clinical chemistry assays.

Thyrotoxicosis factitia masquerading as recurrent Graves' disease: endogenous antibody immunoassay interference, a pitfall for the unwary

Antibody interference in immunoassays is an underestimated problem, which has the potential to cause patient harm and waste health-care resources. We report a case where thyroglobulin antibodies generated a false-positive thyroglobulin result delaying the diagnosis of thyrotoxicosis factitia masquerading as recurrent Graves' disease. A high index of clinical suspicion and good laboratory-clinician communication underpins effective clinical and laboratory strategies to detect potentially erroneous laboratory results due to endogenous antibody interference in immunoassays.

Analytic evaluation of the beta-human chorionic gonadotropin assay on the Abbott IMx and Elecsys2010 for its use in doping control

OBJECTIVES

The principal objective of this study was to compare the analytical performance of the Elecsys2010 (Roche Diagnostics) system with the IMx (Abbott laboratories) system for beta-hCG assay in order to assess its possible utility as a confirmation test for the quantitative measurement of beta-hCG in urine for doping control purposes.

DESIGN AND METHODS

Urine samples with spiked standard known concentrations of beta-hCG and different urine samples from athletes were used in order to determine the calibration curve stability and linearity, detection limit, total, within-run and between-run precision, and method comparison for the IMx and Elecsys2010 systems for beta-hCG assay, along with the stability of samples, at room temperature and at 4 degrees C.

RESULTS

The IMx assay was linear up to 500 IU/L, whereas the Elecsys2010 assay was linear up to 1000 IU/L. The detection limit for the IMx and Elecsys2010 systems were 0.75 IU/L and 0.25 IU/L, respectively. The total precision of the IMx and Elecsys2010 systems were <or=5% for beta-hCG concentrations ranging from 20 to 900 IU/L and from 6.67 to 55.2 IU/L, respectively. The within-run precision tests for the IMx and Elecsys2010 systems yielded CV results of 2-3% and 3-4% respectively, while the between-run precision for the Elecsys2010 was less than 4%, whereas that of IMx was 9-16%. Regression analysis with spiked urine samples yielded the following: slope (SD) 0.7104 (0.003) and y-intercept (SD) -0.4286 (1.397) (Sy.x=2.328; r=0.9999; n=5), whereas regression analysis using the athletes' urine samples yielded the following results: slope (SD) 0.3692 (0.003) and y-intercept (SD) 0.0016 (0.003) (Sy.x=0.0096; r=0.9924; n=100). Sample stability studies evidenced a nonsignificant effect at 4 degrees C and room temperature (25 degrees C) for up to 1 month.

CONCLUSIONS

For doping control, the IMx and Elecys2010 may be used to screen and confirm the presence of beta-hCG in urine of athletes, respectively. Additional studies are needed to verify this finding. This study also underscores the need for beta-hCG assays standardization for doping control.