Evidence against enhanced platelet activity in sickle cell anaemia

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Abstract
Although numerous studies have provided indirect evidence for enhanced platelet activity in sickle cell anemia, little attention was directed to examination of platelet .alpha. and dense granule release in the sickling disorders. By radioimmunoassay plasma levels of the .alpha. granule constituents .beta.-thromboglobulin (.beta.-TG) and platelet factor 4 (PF4) were measured in 43 children with sickle cell anemia in steady state and 24 patients during severe vaso-occlusive crisis. .beta.-TG levels during steady state (50 .+-. 3.6 ng/ml, mean .+-. SEM [standard error of the mean]) were greater (P < 0.001) than in normal controls (36 .+-. 1.6), but there was no additional significant rise during crisis (55 .+-. 5.9). PF4 levels were similar (P = 0.12) in both steady state (10 .+-. 1.2 ng/ml) and crisis (9.3 .+-. 2.3) to those of normal controls (6.0 .+-. 0.8). The similarity of .beta.-TG/PG4 ratios in normal and sickle cell anemia patients as well as the positive correlation (P < 0.05) between platelet count and .BETA.-TG and PF4 suggested that an artefactual in vitro platelet activation was responsible for some of the observed increased .beta.-TG and PF4 levels. Further evidence against enhanced platelet activity in these sickle cell patients included normal intraplatelet content of the dense granule constituent 5-HT [serotonin] and a normal ATP/ADP ratio. Platelet activation in children with sickle cell anemia apparently appears minimal.