Platelet hyperactivity in thalassemia patients with elevated tricuspid regurgitant velocity and the association with hemolysis

Abstract

Introduction: Pulmonary arterial hypertension is a life-threatening complication in thalassemia characterized by elevated pulmonary arterial pressure. Increased platelet activation is associated with this complication; however, its role remains unclear.

Methods: Platelet activation in splenectomized β-thalassemia/hemoglobin E (Hb E) patients was measured using flow cytometric determination of P-selectin and activated glycoprotein (aGP) IIb/IIIa expression, and platelet-leukocyte aggregates (platelet-neutrophil, platelet-monocyte and platelet-lymphocyte aggregates). Tricuspid regurgitant velocity (TRV) was measured and used as an indicator of pulmonary arterial pressure. Plasma hemoglobin served as markers of hemolysis.

Results: Fifteen of 27 patients had elevated TRV (>2.5m/s). Platelet expression of P-selectin and aGPIIb/IIIa, and platelet-leukocyte aggregates were higher in thalassemia patients with elevated TRV than healthy control. Platelet-neutrophil aggregates increased in thalassemia patients with elevated TRV compared to patients with normal TRV. The increase in P-selectin and aGPIIb/IIIa expression induced by adenosine diphosphate (ADP) was higher in patients with elevated TRV than those with normal TRV. Platelet P-selectin expression and platelet-neutrophil aggregates correlated positively with TRV. Plasma hemoglobin levels in patients with elevated TRV were higher than those of the control subjects, and correlated with TRV.

Conclusion: Thalassemia patients with elevated TRV have a further increase in platelet activation that correlates with hemolysis.

Keywords: Hemolysis; Plasma hemoglobin; Platelet; Pulmonary arterial pressure; Thalassemia; Tricuspid regurgitant velocity.