Patients with homozygous sickle cell anemia and alpha-thalassemia have less vigorous hemolysis and run higher hemoglobins than SS patients due to reduced RBC sickling related to a lower hemoglobin concentration within the RBC and higher hemoglobin F levels (Table 13–9). The MCV is low, and the RBCs are hypochromic.
Patients who are compound heterozygotes for betas and beta-thalassemia are clinically affected with sickle cell syndromes. Sickle beta0-thalassemia is clinically very similar to homozygous SS disease. Vaso-occlusive crises may be somewhat less severe, and the spleen is not always infarcted. The MCV is low, in contrast to the normal MCV of sickle cell anemia. Hemoglobin electrophoresis reveals no hemoglobin A but will show an increase in hemoglobins A2 and F (Table 13–9).
Sickle beta+-thalassemia is a milder disorder than homozygous SS disease, with fewer pain episodes but more acute chest syndrome than sickle beta0-thalassemia. The spleen is usually palpable. The hemolytic anemia is less severe, and the hematocrit is usually 30–38%, with reticulocytes of 5–10%. Hemoglobin electrophoresis shows the presence of some hemoglobin A and elevated hemoglobins A2 and F (Table 13–9). The MCV is low.