Interference by iatrogenically induced anti-mouse IgG antibodies in a two-site immunometric assay for thyrotropin

Two-site immunometric assays using mouse monoclonal antibodies are gaining increasingly widespread popularity and use. Patients with circulating antimurine immunoglobulin antibodies capable of interfering in these assays have been encountered and described sporadically. Parenteral administration of murine monoclonal antibodies for imaging and therapeutic purposes is increasing and is known to induce human anti-murine antibodies frequently. We examined 60 serum samples from 48 individuals who received such murine immunoglobulin to determine whether iatrogenically induced anti-murine antibodies could interfere in a two-site (sandwich) immunoradiometric assay for serum thyrotropin. We found that these circulating antibodies can indeed interfere in an "unblocked" assay, but that the interference appears to be suppressed by including nonspecific IgG in the commercial version of the assay kit.