Falsely elevated digoxin level of 45.9 ng/mL due to interference from human antimouse antibody

Transient human anti-mouse antibodies (HAMA) interference in CA 125 measurements during monitoring of ovarian cancer patients treated with murine monoclonal antibody

OBJECTIVE

To investigate the influence of human anti-mouse antibodies (HAMA) on serial CA 125 measurements in serum of patients with epithelial ovarian cancer following single intraperitoneal (IP) therapy with Yttrium-90-labeled human milk fat globule 1 murine monoclonal antibody ((90)Y-muHMFG1) as part of a large international randomized phase III trial.

METHODS

We monitored CA 125 concentrations in longitudinally collected serum samples from 224 patients after IP (90)Y-muHMFG1 (study group) and from 223 patients who received standard treatment (control group). Serum samples of 22 study patients with increased CA 125 concentrations were selected and subjected to affinity chromatography to study HAMA interference in CA 125 measurements.

RESULTS

CA 125 serum concentrations at weeks 1, 4 and 8 were significantly higher in the study group than in the control group. In the first 8 weeks after IP (90)Y-muHMFG1 administration significantly more patients of the study group (144/224) demonstrated CA 125 concentrations above the upper limit of normal of 23 U/mL, as compared to those of the control group (37/223). Affinity chromatography of serum with high CA 125 values in the first 8 weeks confirmed HAMA interference in CA 125 measurements while after 24 weeks this HAMA interference could no longer be detected.

CONCLUSIONS

This is the first study to demonstrate that clinical trials applying murine monoclonal antibodies may be flawed by a transient HAMA effect, which should be considered when monitoring ovarian cancer patients with CA 125 measurements.

Common causes of troponin elevations in the absence of acute myocardial infarction: incidence and clinical significance

Cardiac troponin is a preferred biomarker of acute myocardial infarction (MI). Unfortunately, elevation of troponin can be detected in a variety of conditions other than acute MI. This review focuses on the incidence and clinical significance of increased troponin in conditions commonly associated with troponin elevations, particularly in those that may resemble acute MI.

Inclusion of a non-immunoglobulin binding protein in two-site ELISA for quantification of human serum proteins without interference by heterophilic serum antibodies

Measurement of human serum molecules with two-site ELISA can be biased by the presence of human heterophilic anti-animal immunoglobulin antibodies (HAIA) that cause false-positive signals by cross-linking the monoclonal (mAb) and/or polyclonal antibodies (pAb) used for the pre- (capture) and post-analyte steps (detection). To evaluate a novel ELISA format designed to avoid interference by HAIA, a target-specific non-immunoglobulin (Ig) affinity protein (affibody) was used to replace one of the antibodies. First, a human IgA-binding affibody (Z(IgA)) selected by phage display technology from a combinatorial library of a single Staphylococcus aureus protein A domain was used. The detection range of IgA standard using an ELISA based on Z(IgA) for capture and goat pAb against IgA (pAb(IgA)) for detection was comparable with that of using pAb(IgA) for both capture and detection. Secondly, another affibody (Z(Apo)) was combined with mAb and used to detect recombinant human apolipoprotein A-1. The affibody/antibody ELISAs were also used to quantify human serum levels of IgA and apolipoprotein A1. To verify that human serum did not cause false-positive signals in the affibody/antibody ELISA format, the ability of human serum to cross-link affibodies, mAb (mouse or rat) and/or pAb (goat) displaying non-matched specificities was assessed; affibodies and antibodies were not cross-linked whereas all combinations of mAb and/or pAb were cross-linked. The combination of affibodies and antibodies for analysis of human serum molecules represents a novel two-site ELISA format which precludes false-positive signals caused by HAIA.

Towards a better understanding of heterophile (and the like) antibody interference with modern immunoassays

BACKGROUND

Heterophile antibodies interfere with immunoassays. Understanding the nature and characteristics of these antibodies provides a format for better identifying and removing them. Growing evidence suggests many of these antibodies are natural antibodies. Very large number of tests are being performed with automated analyzers and there has been a problem with misdiagnosis due to interference. New commercial agents for blocking heterophile antibodies have been developed.

METHODS

Review of the immunology and methodological literature with critical interpretation of the findings.

CONCLUSIONS

Heterophile antibodies consist of natural antibodies and autoantibodies. Both types are usually weak antibodies that interfere by noncompetitive mechanisms. Based on very strong circumstantial evidence, we propose that natural antibodies account for most interference with automated immunoassays. In terms of false positive results, the interference rate is very low, about 99.95% accuracy. Specific blocking agents have some theoretical advantage over nonspecific blocking agents, but in actual practice, the very low false positive frequency makes it difficult if not impossible to statistically compare blocking agents or other assay modifications with adequate statistical power. In the absence of a technique that lends itself to automation for removing all immunoglobulins, it appears that infrequent heterophile interference cannot be avoided.

Performance of a Revised Cardiac Troponin Method That Minimizes Interferences from Heterophilic Antibodies

Background: Recent guidelines for use of cardiac troponin to detect cardiac damage and for cardiovascular risk stratification have made increasingly sensitive troponin assays important. Troponin assays continue to be plagued by interferences caused by heterophilic antibodies (HAs). We evaluated the performance of a revised cardiac troponin I (cTnI) assay designed to have increased analytical sensitivity and to minimize the effect of HAs.

Methods: The revised Dade Behring Dimension® cTnI assay was evaluated according to NCCLS EP5-A at five institutions. Plasma samples from 14 309 patients were assayed by the original Dimension cTnI assay. To identify samples that may have interfering HAs, samples with values >1.4 μg/L were reanalyzed on the Dade Behring Stratus® CS cTnI assay. Samples with possible interfering antibodies were also analyzed before and after selective absorbance studies on the revised Dade Behring Dimension cTnI assay.

Results: The limit of quantification in the revised method was 0.1 μg/L with imprecision (CV) of 11–17% at 0.1 μg/L. Values correlated well with the Stratus CS cTnI method: revised = 1.06(original) + 0.01; r = 0.98, Sy|x = 0.25 μg/L). Falsely increased results consistent with myocardial infarction by the original Dimension cTnI assay and presumably attributable to HAs were identified in 0.17% of all patients with samples submitted for cTnI analysis. The revised Dimension cTnI assay eliminated the interference in 17 of 25 samples identified and greatly decreased the interference in the other 8.

Conclusions: The revised Dimension cTnI method greatly minimizes the effect of interfering HAs. It also exhibits analytical performance characteristics consistent with recent guidelines for use of this assay to detect cardiac damage.