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.

The value of proteomics for the diagnosis of a platelet-related bleeding disorder.

Familial bleeding problems are frequently difficult to diagnose because currently used clinical tests cannot identify intracellular molecular defects of platelets. Using platelet proteomics, a comprehensive analytical tool, we diagnosed a family with severe bleeding problems of unknown origin with Quebec Platelet Disorder. Prior to proteomic analysis, we determined platelet counts, presence of glycoprotein (GP) Ib and GPIIb/IIIa, platelet aggregation, dense granule content and release, plasma levels of fibrinogen, Factor XIII and fibrin degradation products in four family members. Abnormalities were detected in platelet aggregation studies, which revealed variably reduced responses to ADP, collagen and epinephrine with concomitantly decreased ATP/serotonin secretion. In addition, D-dimer levels were significantly elevated 72 hours after in vitro thrombin stimulation of platelet-rich plasma. Together with the autosomal dominant inheritance and the delayed onset of bleeding in two of the four patients these results did not support any known platelet disorder. Therefore, the proteome of platelet lysates separated by one-dimensional SDS-PAGE was analysed by liquid chromatography-tandem mass spectrometry (LC-MS/MS). Platelet proteomics showed reduced amounts of alpha-granule proteins multimerin, fibrinogen and thrombospondin-1 in patient compared to control samples suggestive of Quebec Platelet Disorder. The diagnosis of Quebec Platelet Disorder was confirmed by urokinase-specific Western blots. Urokinase causes the degradation of alpha-granule proteins in this disorder. Diagnosis of rare bleeding disorders has important implications for prophylactic and acute treatment of bleeding patients. This is the first report using proteomics to identify a familial platelet defect.