Use of monoclonal Jk^a and Jk^b reagents in phenotyping red cells with a positive direct antiglobulin test

Twenty-five red cell samples with a positive anti-IgG direct antiglobulin test (DAT) were tested with human monoclonal IgM Jk^a and Jk^b antibodies. Red cell samples were first tested by a 5-minute incubation tube test with the monoclonal antibodies (MAbs). The same red cells were then chloroquine diphosphate (CDP)-treated, and retested. Eleven of the CDP-treated samples were also tested with conventional polyclonal antibodies (PAbs) that required a 37°C incubation for 30 minutes, followed by an indirect antiglobulin test. The Jk^a and Jk^b MAbs consistently gave the same phenotype results both on untreated DAT-positive red cells and on the same cells after CDP treatment. Two of the CDP-treated samples had diminished antigen expression with the MAbs, a finding that may have been caused by the CDP treatment. One untreated sample, which spontaneously agglutinated in a low-protein medium, was incorrectly phenotyped with the anti-Jk^a MAb, but both MAbs and PAbs gave the same correct results with the CDP-treated cells. These findings illustrate that the use of Jk^a and Jk^b MAbs in phenotyping DAT-positive specimens is practical and beneficial. Immunohematology 1994;10:16.