Who Keeps Changing My Results? - A Case of Heterophile Antibody Interference

Abstract Introduction/Objective Heterophile antibodies are known to cause interference in immunoassays leading to misleading results causing diagnostic confusion and unnecessary testing and/or treatment. Many clinically important analytes are tested using antibody-based assays, as such, these are prone to interference. Methods/Case Report We describe a case of a 73 year old male who was referred with history of hypocalcemia and his previous lab tests were suggestive for idiopathic hypoparathyroidism, Hashimoto’s disease and Addison’s disease raising physician concern for a possible Type 1 autoimmune endocrinopathy. One of his results (cortisol) was outside the analytical measurement range and hence the sample was diluted and tested again, but the result was much less than what was expected, prompting an investigation. Investigation for an interfering substance included serial dilution and analysis of the same sample for the same analytes by different methods (different immunoassay, mass spectrometry or both). Based on non-parallelism in serial dilution results, discordant results with other methods, and loss of interference after dilution it was determined that the most likely cause was a heterophile antibody. Results (if a Case Study enter NA) NA Conclusion Awareness of the possibility that interference by heterophile antibodies can lead to erroneous laboratory results is important to prevent unnecessary testing and inappropriate diagnosis/management.