Investigation of interference from canine anti-mouse antibodies in hormone immunoassays

Background Canine anti-mouse antibodies are a potential source of immunoassay interference, but erroneous immunoassay results are not always easily identifiable. Anti-Mullerian hormone (AMH) is a marker for the presence of gonads in dogs, but elevated AMH concentrations in neutered dogs could also be caused by antibody interference. For other assays, a discrepant result obtained after antibody precipitation might indicate antibody interference. Objectives We aimed to evaluate if canine anti-mouse antibodies are a source of erroneous results in the AMH assay and if antibody precipitation with polyethylene glycol (PEG) is a useful tool for detecting antibody interference in a variety of immunoassays used in the veterinary clinical laboratory. Methods Twenty-nine positive and 25 negative samples for anti-mouse antibodies were analyzed for AMH, canine total thyroxine (TT4), canine thyroid-stimulating hormone (TSH) and progesterone before and after treatment with PEG. Results that differed by more than four SDs from the intra-assay coefficients of variation were considered discrepant. Elevated AMH concentrations in neutered dogs with anti-mouse antibodies and no visible gonads present were considered evidence of interference. Results Evidence of antibody interference was found in two samples analyzed for AMH. The presence of anti-mouse antibodies did not lead to a higher proportion of discrepant results after PEG treatment for any of the immunoassays. The overall incidence of discrepant results for healthy controls was very high (73%). Conclusions Canine anti-mouse antibodies are a source of erroneous AMH results. Antibody precipitation with PEG is not a useful tool for detecting interference caused by such antibodies.