Steady-state platelet count and complications of sickle cell disease.

The current model of vaso-occlusion in sickle cell disease (SCD) views the process as a result of interaction between the cellular components of blood and the vascular endothelium. The clinical importance of the number/proportion of erythrocytes containing haemoglobin S in people with SCD has been traditionally recognized from the ecacy of exchange blood transfusion in the prevention and treatment of major complications such as stroke or acute chest syndrome. Similarly, the clinical signi®cance of leucocyte count in SCD is illustrated by the observations from various studies that disease-related morbidity and mortality increase with the number of white blood cells. ± 5 By contrast, the e€ect of platelet count on the clinical manifestation of SCD is not so well established. A single previous study noted an association between stroke in SCD and platelet count 4450610/l. The aim of this study was to ®nd out if the number of complications of SCD is related to steady-state platelet count. With the Coulter STKS automatic blood analyser, platelet count was determined in steady-state SCD, a minimum period of two months after sickle cell crisis, in 101 HbSS adults of black African ancestry for whom the normal range is 100 ± 300610/l. Individuals with the following were excluded from the study: any disease in addition to SCD, pregnancy/childbirth in the previous three months, and HbF level 510%. The rationale was to minimize the confounding e€ect of conditions that in ̄uence platelet count or the clinical severity of SCD. The complications of SCD in each individual were ascertained from clinical assessment, investigations, and hospital records. The complications observed and number of people a€ected were: avascular necrosis of joints (28), gallstones (27), nephropathy (25), priapism (18), stroke (12), acute osteomyelitis, chronic leg ulcer, chronic liver insuciency (8 each), acute chest syndrome (7), chronic sickle lung (6), retinopathy (4), pulmonary hypertension and endocrinopathy (2 each). Thirty-®ve (35) subjects had one complication of SCD, 20 had two complications, 13 patients had three complications, seven had four complications, two had ®ve complications, and one had six complications. The mean platelet count and the percentage of subjects who had thrombocytosis in steady-state were not signi®cantly di€erent between patients with and without complications of SCD (P40.1). Steady-state platelet count and the proportion of subjects who had thrombocytosis were also comparable between people with stroke and those without complications (see table 1). Linear correlation coecient (r) between platelet count and number of complications of SCD was low at 0.085. The ®ndings suggest that steady state platelet count does not have a clinically signi®cant relationship with the number of complications of SCD.