The sensitivity, specificity, and clinical relevance of gel versus tube DATs in the clinical immunology laboratory

The DAT is a test used to demonstrate in vivo antibody and/or complement coating of RBCs. Typically, the DAT is performed in test tubes; however, recently a number of commercially available tests using gel-filled microtubes have become available. Few data comparing the sensitivity of these test media are available. To compare the rate of detection of a positive DAT performed in test tubes versus in gel-filled microtubes and to assess the clinical significance of the results in patients undergoing evaluation of anemia, we tested 310 consecutive EDTA-anticoagulated blood samples from adult patients. The samples were analyzed using both the conventional tube technique and a gel-based assay (DiaMed^®; Cressier sur Morat, Switzerland). Test results were expressed as either positive or negative. When a positive result by either technique was encountered, the treating physician was interviewed to determine whether the result warranted further patient investigation or treatment. In 268 out of 310 cases the DAT was negative by both methods. Of the 42 patients with a positive DAT, the test was positive by both methods in 18 patients. In the remaining 24 cases the DAT was positive by the gel test only. In all cases positive by both techniques the test result affected patient management. Of the 24 cases that were positive only by gel test, 3 were judged to be clinically significant. In this study, the gel test was more sensitive than the tube technique for performance of the DAT. However, the clinical significance of a DAT positive only by a gel test is doubtful. We believe that use of the gel-based DAT should be more extensively evaluated before it is adopted as a standard technique in general clinical laboratory practice.