Serum volumes should not be reduced when testing neonates for unexpected red cell antibodies.

Serum-to-red cell ratio (volume:volume) significantly affects the sensitivity of antibody detection. Obtaining sufficient serum quantity can be a problem when testing blood from transported neonates not accompanied by maternal samples. Reducing serum volumes used for testing might result in missed antibodies. The authors studied 1,177 sera for unexpected red cell antibodies by comparing one versus two drops of patient serum using a technique with LISS at 37 degrees C through the antiglobulin phase. The serum-to-red cell ratio using two drops was approximately 50: 1. Results of 60% (58/96) of samples containing antibody benefited by the use of increased serum. Eighteen percent; (17/96) had antibodies detected only with two drops that were missed entirely by one, and 43% (41/96) showed stronger positive reactions using two drops versus one. Importantly, antibodies detected only with or enhanced by two drops were clinically significant (anti-D, anti-K, anti-M, anti-c, anti-E). Thus, reducing serum-to-cell ratio is potentially dangerous, and blood banks should insist on adequate sample size to ensure patient safety.