IgA and IgM human immunodeficiency virus antibodies in weakly reactive or false-negative blood donors.

Detection of antibodies to the human immunodeficiency virus (HIV) in recently infected donors is crucial to prevent the transmission of HIV infection via blood products. To determine whether specific antibodies of the IgA or IgM class are present as markers of recent infection in donor specimens that have borderline reactivity on routine enzyme immunoassay (EIA) screening, 15 specimens that were positive by immunoblot were tested for IgA and IgM HIV antibodies. All 15 had detectable IgA HIV antibodies, and 14 had IgM HIV antibodies. The 15 specimens were tested further, each by two independent laboratories, with nine licensed EIAs. Two of the nine EIAs found all 15 units positive in both laboratories; seven EIAs found 1 to 5 of the 15 units negative, for a total of 31 false-negative results. The results indicated a difference between the sensitivity of EIA kits using only anti-IgG reagents and of kits using multispecific reagents that react with IgG and other classes of antibody. In a modified procedure, the addition of enzyme-conjugated anti-IgA or anti-IgM to the kit's enzyme-conjugated reagent increased the optical density values of most false-negative specimens to the positive range. It was concluded that licensed kits vary in reactivity with IgA and IgM HIV antibodies and that sensitivity could be increased by improved detection of these classes of antibody.