Variable degrees of suppression of hemoglobin S synthesis in subjects with hemoglobin SS disease on a long-term transfusion regimen.

The objectives of this study were to quantify the amount of blood required to suppress synthesis of hemoglobin S (HbS) in patients with hemoglobin SS on a long-term transfusion regimen and to evaluate factors that might contribute to variations in transfusion-induced patterns of responsiveness. Eleven patients with hemoglobin SS (age range, 2 years 4 months to 19 years 9 months) who had had a cerebrovascular accident were monitored during a period of 1 1/2 to 4 years for HbS percentages, reticulocyte percentages, the amount of erythrocytes infused, and weight. From these data the amount of blood necessary to maintain the HbS concentration at less than 30% was expressed as units of packed erythrocytes administered per week per kilogram of body weight. Percentage of HbS were significantly lower in three subjects than in the other eight (6.1 +/- 0.6 vs 23.0 +/- 2.1; p = 0.0009) as were the reticulocyte percentages (2.9 +/- 0.3 vs 7.9 +/- 0.7; p = 0.0021). However, there were no significant differences between pretransfusion hematocrit (0.278 +/- 0.012 vs 0.281 +/- 0.01; p = 0.90) and units of erythrocytes given per week per kilogram (0.0147 +/- 0.0008 vs 0.0156 +/- 0.0009; p = 0.58). Factors explored to define the reason that HbS synthesis was more easily suppressed in some patients than in others included measurements of serum chemistry values and erythropoietin, identification of erythrocyte alloantibodies, and a survey for Howell-Jolly bodies. No significant differences were seen. Although the reasons for the marked variation in transfusion-induced depression of HbS synthesis are unclear, this study emphasizes the importance of determining the units of packed erythrocytes needed per week per kilogram and correlating this value with the pretransfusion HbS percentage. By doing so, one can select the minimal amount of blood necessary to achieve the desired HbS percentage and thereby decrease the risks of transfusion.