Prevalence of Heterophilic Antibody Interference in Eight Automated Tumor Marker Immunoassays

Abstract

Heterophilic antibodies are human antibodies that can bind animal antibodies. They can cause problems in immunoassays, particularly immunometric assays, where they can form a bridge between the capture and detection antibodies, leading to a false-positive result in the absence of analyte or, if analyte is also present, to a false increase in measured concentrations. Very rarely, heterophilic antibodies can also lead to false-negative or falsely low results. By adding blocking reagents, assay manufacturers have reduced the incidence of heterophile interferences from the 2–5% observed in unblocked assays but have been unable to completely eliminate the problem (1)(2). During the last 10 years, tumor marker assays for human chorionic gonadotropin (hCG), prostate-specific antigen (PSA), cancer antigen 125 (CA 125), carcinoembryonic antigen, and calcitonin have all been reported to suffer from this problem, frequently with undesirable clinical outcomes (3)(4)(5)(6)(7). In our own laboratory we noted that our thyroglobulin assay displayed a higher than acceptable rate of heterophile interference (8). Although we were able to rectify this problem through pretreatment of samples in heterophile blocking tubes (HBT) (8), we became concerned that some of our other tumor marker assays may suffer from similar problems. We therefore decided to systematically evaluate all of our tumor marker assays for evidence of interference from heterophilic antibodies. Our laboratory performs the following tumor marker assays: calcitonin on the Nichols Advantage, gastrin on the Immulite2000, CA 125 and cancer antigen 15-3 (CA 15-3) on the Vitros ECi, and α-fetoprotein (AFP), hCG, total PSA, and free PSA on the Beckman Access. All of these assays use at least one mouse monoclonal antibody (Table 1⇓ ). We designated the maximum tolerable heterophile interference rate for any of these assays as 0.5% and started collecting samples prospectively. Power calculations …