Immunoassay interference by human antianimal antibodies is well documented and continues to plague current immunometric assays. Antibody interference is not limited to 2-site noncompetitive immunoassays; it can also occur in competitive immunoassays. The interfering antibodies can produce either high or low assay results, depending on assay format and the species and/or specificity of the antibody or antibodies used. The incidence of antianimal antibodies varies widely among studies and ranges from 0.3% to 4% in an unselected population. The incidence in patients receiving animal immunoglobulins for medicinal purposes ranges from 41% to 80%.
The term “antianimal antibodies” is used when there is a history of treatment with animal immunoglobulins, and they tend to be monospecific, high-affinity antibodies. In contrast, heterophile antibodies are associated with no known exposure to animal immunoglobulins and typically display weak reactivity against multiple animal proteins. Although the incidence of antianimal and heterophile antibodies in clinical samples exceeds 40%, the majority are low-affinity antibodies that do not interfere in immunoassays. Manufacturers also add blocking agents to their immunoassays to help prevent antibody interference.
Once a discordant immunoassay result is suspected, a review of the patient's appropriate clinical history and a discussion with the patient's clinician should occur as part of the investigation. A nonlinear response after sample dilution can be used to demonstrate antibody interference; however, some interfering antibodies are linear upon dilution, so this test does not always rule out antibody interference. As illustrated in this clinical case, heterophile antibody blocking tubes can be used to eliminate the interference, although this approach does not always eliminate the interference. For documented cases of exposure to animal immunoglobulins, a different assay method or an immunoassay that uses different animal antibodies should produce reliable results. It is essential for laboratorians to understand the limitations of immunoassays and to work closely with clinicians when results do not agree with clinical findings.
Author Contributions: All authors confirmed they have contributed to the intellectual content of this paper and have met the following 3 requirements: (a) significant contributions to the conception and design, acquisition of data, or analysis and interpretation of data; (b) drafting or revising the article for intellectual content; and (c) final approval of the published article.
Authors' Disclosures or Potential Conflicts of Interest: No authors declared any potential conflicts of interest.
Role of Sponsor: The funding organizations played no role in the design of study, choice of enrolled patients, review and interpretation of data, or preparation or approval of manuscript.
- Received for publication December 7, 2010.
- Accepted for publication December 14, 2010.
- © 2011 The American Association for Clinical Chemistry