HETEROPHILIC ANTIBODIES REMAIN A PROBLEM FOR THE IMMUNOASSAY LABORATORY

The prevalence of heterophilic antibody interference in a modern immun ochemiluminometric assay containing blocking agents was determined usi ng thyrotropin as an illustrative example. Serum samples were obtained from 295 consecutive patients who underwent routine thyroid function testing. The following versions of the thyrotropin assay were used: pr otocol A (zero blocker), protocol B (routine blocker concentration), a nd protocol C (extra blocker). Ten patients (prevalence 3.4%) had sign ificant levels of heterophilic antibodies (protocol A value greater th an 9 SD from the protocol B value). The observed thyrotropin levels fo r protocols B and C were the same for all patients, consistent with th e reagent blockers in routine assays adequately eliminating heterophil ic antibody interference. However, seven more patients (0.03%) in a se ries of 21,000 assessed by routine thyroid function testing had discor dant results because of a concentration of heterophilic antibodies so high as to overwhelm the added blocking agents.