Erroneous automated optical platelet counts in 1-hour post-transfusion blood samples.

Thrombocytopenic patients with acute leukemia may show high post-transfusion count increments that significantly exceed the number of transfused platelets. This study demonstrates that the automated hematology analyzer Sysmex XE-2100 reports erroneously high optical platelet counts when the blood sample contains particles in the size range of platelets or smaller. Thrombocytopenic or low-normal whole blood samples were spiked with 1 mum latex beads (n = 14) to mimic contaminants under controlled conditions. Optical and impedance measurements of spiked and control samples with the Sysmex XE-2100 were compared with the Advia 120 and the manual counts. The added beads unexpectedly increased the automated optical platelet counts in the Sysmex XE-2100 and, to a lesser extent, the Advia 120 (Wilcoxon signed ranks test, P < 0.05), while the beads were not included in the impedance or the manual microscopic platelet counts. Differential interference contrast microscopy was used to investigate samples from platelet concentrates for transfusion. Platelet concentrates (32/128) were identified as possible sources for particles that were microscopically distinct from platelets but would be included in the automated optical count. Transfusion of platelet concentrates containing contaminating particles can lead to unexpectedly high post-transfusion platelet counts and misdiagnosis of thrombocytopenic patients.