The effect of fetal hemoglobin on the sickling dynamics of SS erythrocytes.

A reaction-limited flow system was used to study the effects of several hematological variables on the sickling dynamics of homozygous SS erythrocytes. Sudden deoxygenation was achieved via a zero oxygen tension sodium dithionite solution; the erythrocytes were recorded on video tape and sickling was identified by morphologic criteria. Two indices of the sickling process were determined: t50, the time at which 50% of the initially discoid cells had sickled; %3sec, the percentage of sickled cells 3 s after the start of deoxygenation. The percentage of fetal hemoglobin (Hb F) significantly influenced these indices with increasing levels of Hb F yielding longer t50 times and smaller %3sec values. Calculated values of percentage F-erythrocytes also showed significant correlations with the two sickling indices. Neither single nor stepwise multiple regression techniques demonstrated any significant effects of percentage hemoglobin A2, mean corpuscular hemoglobin, mean corpuscular hemoglobin concentration or mean corpuscular volume. The non-significant effects of these variables may be related to their somewhat narrow range observed in the patient population and to the dominating influence of Hb F levels.