812 PLATELET ACTIVATION IN SICKLE CELL DISEASE

Abstract

Abnormalities in platelet number and function have been described in patients with homozygous sickle cell disease (SS), suggesting that platelets play a role in this disorder. We studied platelet shape and circulating platelet aggregates (AGG) in SS patients as a guide to in vivo activation. One drop of freely flowing blood was collected by venipuncture into a siliconized vial containing 1% glutaraldehyde in 0.38% citrate. Using phase microscopy, 200 platelets were examined to see whether they were deformed (DEF) (spherical shape with ≥ 1 spinous process), AGG (≥ 2 adherent DEF platelets), or in their natural discoid shape. Results were expressed as % activated, computed as 100 × (DEF + AGG)/total. Thirty pediatric patients (ages 1-18 years) with a diagnosis of SS or SC disease were evaluated and found to have a mean activation of 65.3 ± 26.9% (1SD). A normal population of 15 adults had a mean of 22 ± 8.8% (P ≤ 0.001). Age, recent vasoocclusive crisis, pneumonia, aspirin, and chronic transfusion therapy were separately analyzed and found not to have a significant effect. A 4-year-old with SS was studied before, during, and after transfusion therapy for debilitating recurrent crises. Activation corrected from a baseline of 88% prior to therapy to 25% following 6 mos. of transfusions, but gradually returned to 65% at the time of the first crisis following the cessation of transfusions. These observations further indicate that platelets are involved in the pathophysiology of sickle cell disease.

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