Variable levels of carry over on platelet counts < or = 20 x 10(9)/l with the Bayer Advia 120.

Accurate platelet counts are essential for the safe management of severe thrombocytopenia (platelet counts < or = 20 x 10(9)/l). The effect of carry over on platelet counting in severe thrombocytopenia was investigated by performing counts before and after saline rinses on three Bayer Advia 120 automated blood counters. Counts were performed in both primary and manual closed tube system modes on two instruments and in manual open tube mode on a third. A total of 194 samples with platelet counts < or = 20 x 10(9)/l were studied. First counts were significantly higher in all groups. The magnitude of the difference varied both by analyser and counting mode. Carry over was minimal with one analyser in primary mode and second counts were on average only 5.5% lower; on a second analyser in manual closed tube system mode second counts were on average 37.7% lower. A first count of > or = 10 x 10(9)/l fell to <10 x 10(9)/l on the second count in 35 of 145 samples (24.1%). In five such samples, all tested on one analyser, the second count was <50% of the value of the first count. Two of 49 (4.1%) first counts of <10 x 10(9)/l increased to > or = 10 x 10(9)/l on repeat. These results show a variable and often potentially clinically important carry-over effect on severely thrombocytopenic samples using the Advia 120.