False Positive Tests for Hepatitis-Associated Antigen in Blood Donors Caused by Antibodies to Ruminant Serum Proteins

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Abstract
A reaction of non-identity observed during routine screening for hepatitis associated antigen (HAA) by agar gel diffusion led to the demonstration that bovine thrombin added to hepatitis screening reagents could react with antibodies present in normal donor sera. Similar false positive reactions for HAA occurred when anti-HAA produced in ruminants was employed. These human anti-ruminant antibodies occurred in 0.19% of 15,632 blood donors from two geographic areas. The human antibodies were IgG γ globulins and reacted primarily with ruminant serum IgG and IgM. They also reacted with IgG and IgM present in milk plus additional unidentified milk proteins. The anti-ruminant antibodies were present in 39% of IgA deficient patients; among “normal” donors found to have such antibody, 11.5% had depressed levels of IgA. The majority of donors with anti-ruminant antibodies, however, had normal serum IgA concentration. Secretory IgA was present in those tested. The presence of anti-ruminant antibodies in donor sera will produce false positive reactions for HAA and/or anti-HAA in agar gel diffusion (AGD) if “thrombinized” or ruminant-derived reagents are used and will cause false positive reactions for anti-HAA in counterelectrophoresis. Such antibodies do not interfere with complement fixation or hemagglutination tests for hepatitis antigen or antibody.

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