Comparative testing for weak expression of D antigen: manual tube testing vs. a semiautomated IgG gel system

Donor RBCs nonreactive in initial tests for D must be tested further for evidence of weak expression of D antigen. Performing this test in test tubes is labor intensive and prone to inconsistencies in readings (relative strength of agglutination) and interpretation (positive versus negative). These inconsistencies can lead to repeat testing, additional documentation, and delay in releasing units. We evaluated use of the Tecan MEGAFlex-ID pipettor to perform this test in anti-IgG gel cards. Results with this semi-automated gel test were compared with results obtained with 37 D- and 99 weak D samples, as determined by previous testing with a manual IAT tube test. Hands-on time was determined for both methods and both methods were evaluated for inconsistency, or nonagreement, between the interpretation of the current weak D test and the results on record for any prior donations. There were no discordant results obtained, with the majority of weak D samples giving stronger reactions with the gel test. The semiautomated gel test required less hands-on time, with an average savings of more than 70 seconds per test. There were no inconsistencies with the gel method, whereas manual tube testing was found to have an inconsistency rate of 0.035 percent of total samples tested. Semiautomated IgG gel is now used for all weak D testing, with a labor savings of more than 10 hours per week. Thus far, more than 70,000 donors have been tested, with no inconsistencies reported.