How slow can you be when performing a direct antiglobulin test?

While continuous performance is preferred for any assay, trans-fusion services are particularly susceptible to interruptions that may interfere with testing. If these interruptions occur after the red blood cell (RBC) suspension is made or after the last wash is decanted, direct antiglobulin test (DAT) results may be affected. This study aimed to assess if delays at these two procedural steps compromise DAT results. Samples with positive DATs (up to 2+) using anti-IgG (IgG-DAT) were included. RBC suspensions (2-5%) were prepared from unwashed RBCs or RBCs washed once. These suspensions were used to perform tube IgGDATs without delays to obtain baseline results. IgG-DATs were repeated with delays after preparation of the RBC suspension (1, 5, 15, 30, and 60 minutes) or after the last wash decant (1, 5, 15, or 30 minutes). Three anti-IgG reagents were used: Anti-IgG (Murine Monoclonal) Gamma-clone; Werfen, Barcelona, Spain; Anti-IgG (Rabbit); QuidelOrtho, Raritan, NJ; and AHG Anti-IgG; Bio-Rad, Hercules, CA. Samples were considered impacted if their IgG-DAT strength differed by two or more reaction grades from baseline. The analysis included 25 samples. Samples with baseline IgG-DAT results of 1+^s and 2+ were determined to not be impacted. Three samples were weakened by delays after RBC suspension preparation. One sample was weakened when the addition of anti-IgG was delayed. While most samples with weakly positive baseline IgG-DAT results were not impacted, the samples with the weakest baseline IgG-DAT results were impacted more frequently than those with stronger baseline IgG-DAT results. Because it is impossible to predict which samples will not be impacted by delays in these testing steps, DAT procedures should be performed with minimal interruption.