Predicted probability from the multivariate logistic model of abnormally high velocities. Abnormally high velocities (≥ 2 m/sec) as a function of LDH (A) or hemoglobin level (B) in different patient groups. Patients with isolated α-thalassemia associated with normal G6PD (n = 90) are represented by green lines; patients with isolated G6PD deficiency without α-thalassemia (n = 13) by black lines; and patients with G6PD deficiency and α-thalassemia (n = 114) by red lines. Blue lines represent patients with neither G6PD deficiency nor α-thalassemia. The probability of abnormal TCD increases with low hemoglobin levels and, more importantly, with the degree of hemolysis.