Platelet P-selectin and platelet mass, volume and component in sickle cell disease: relationship to genotype

Excess platelet activation (e.g. increased soluble P selectin [sPsel] and beta thromboglobulin [beta-TG]) is well established in sickle cell disease (SCD) and may contribute to the prothrombotic/hypercoagulable state and vascular occlusion characteristic of the disease. We hypothesised altered whole platelet P-selectin (pPsel), and morphological platelet indices mass, volume and component in SCD and two of its major genotypes.

We recruited 35 SCD patients [mean age 31 years, 54% men]. Of these, 16 had homozygous sickle cell (HbSS) disease and 19 had sickle-haemoglobin-C (HbSC) disease. Patients were compared with 29 subjects with normal haemoglobin (HbAA) matched for age and ethnicity. Platelet mass, volume and component were measured by flow cytometry, pPsel in platelet lysate, sP-sel and beta-TG by ELISA.

SCD patients had lower pP-sel and mean platelet volume (MPV) but elevated platelet component (MPC), and, as expected, elevated platelet count, and sP-sel (all p<0.05) compared to HbAA subjects. In both groups, pPsel correlated with MPV, and MPV correlated positively with mean platelet mass (MPM) and negatively with MPC. sPsel correlated with platelet count only in SCD, not in the controls. Platelet count alone was different (higher) in HbSS compared to HbSC, and sPsel correlated with platelet count only in HbSC disease, not in HbSS disease.

Patients with SCD have various abnormalities in their platelets regardless of genotype: there are more numerous platelets, which are smaller, contain less P selectin per cell, but have a higher concentration of granules than those of HbAA subjects. These differences may mark and/or promote the prothrombotic state in SCD.