The significance of a positive direct antiglobulin test: Comparison between the microcolumn method and conventional tube method

Kim, Hyun Soo; Lee, Kyung; Lee, Do Hoon

Abstract

BACKGROUND: The direct antiglobulin test(DAT) is a method detecting red cell-coated antibodies, much of which are related to immune hemolytic anemia. The microcolumn method-direct antiglobulin test(MC-DAT) is known to be more sensitive and convenient than conventional tube method-direct antiglobulin test(T-DAT). We compared the results of both DAT methods and evaluated the relationship between positive DAT result and immune hemolytic anemia.
METHODS
Ninety-three subjects were classified into three groups according to clinical diagnosis, hemoglobin level, and serum IgG level; 15 healthy controls(group I), 8 patients without anemia and with total IgG greater than 1800 g/dL(group II), and 69 anemic patients with hemoglobin less than 10 g/dL(group III). DAT was performed on the EDTA-anticoagulated samples of these patients using both microcolumn method and tube method. Additional tests for hemolytic anemia were performed when either the result of MC-DAT or T-DAT was positive, and diagnosis of hemolysis was divided into three categories: hemolysis(category A), undetermined(category B), and no hemolysis(category C).
RESULTS
Of total 93 samples, 18 were positive and 48 were negative with both DAT methods. Twenty-seven samples showed positive results by MC-DAT and negative by T-DAT, while none showed to be negative results by MC-DAT and positive by T-DAT. The agglutination strength of MC-DAT was stronger than that of T-DAT. Five samples which could be categorized to category A showed positive results by MC-DAT and negative by T-DAT. Two samples showing positive results with both methods but which were categorized to category C could be found in group II.
CONCLUSIONS
The microcolumn method(MC-DAT) seems to be more sensitive than the tube method. However, diagnosis of immune hemolytic anemia based on the DAT result needs much caution because both methods can be influenced by high serum IgG concentration and these can show false positive results.