Mean Platelet Volume in Children with Sickle Cell Disease on Chronic Transfusion Therapy.

The symptoms in sickle cell disease are related to ischemic/vaso-occlusive episodes involving the bones, spleen, brain and lungs. One of the possible mechanisms for vaso-occlusion is platelet activation and increased platelet reactivity which is demonstrated by increased platelet volume resulting in an elevated platelet distribution width. We hypothesized that chronic transfusion therapy given to patients with recurrent severe ischemic episodes and/or stroke may lower mean platelet volume (MPV) in addition to decreasing hemoglobin S. We performed a retrospective chart analysis of all patients with sickle cell disease who were on a chronic transfusion regimen at Schneider Children’s Hospital between January 1995 and March 2005. Out of 60 eligible patients, only 42 were eligible for this study. The remaining patients were excluded for less than 3 transfusions in total or incomplete records. The data retrieved included age and sex of the patient, type of sickle cell disease, indication for chronic transfusion therapy, duration of transfusions and blood count variables during the three phases, i.e. prior to, during and after transfusion therapy. The variables included hemoglobin, mean cellular volume, platelet count, reticulocyte count and MPV for each patient with a minimum of one value in each phase. As many values were recorded based on the availability in the records, with at least an interval of 3 months between each blood count and at least 3 months apart from a transfusion.

Results: Sixty-four percent were males and 95% had HbSS genotype. The major indication for transfusion therapy (85%) was stroke. Mean values of each variable and their ranges were compared across the 3 periods using the Kruskal Wallis test. Although the platelet count decreased significantly during transfusions compared to pre-transfusion period, the mean value of MPV did not differ across the 3 periods with a range between 5.9 and 11.3 in all the 3 periods. Furthermore, using the Anacova method proposed by Bland and Altman, there was an overall significant negative correlation between MPV and platelet count, while no correlation at all was present between MPV, reticulocyte count and hemoglobin in any of the 3 periods. Our findings suggest that multiple transfusions do not alter platelet size or volume, which indirectly may indicate that there is no change in platelet function or activity in these patients on chronic transfusion therapy. The changes in MPV values seen in this study are real, as they follow the natural thrombokinetics by maintaining a negative correlation with the platelet count during all 3 periods.