Foetal haemoglobin in homozygous sickle cell disease: a study of patients with low HBF levels.

High foetal haemoglobin (HbF) levels are believed to ameliorate the manifestations of homozygous sickle cell (SS) disease. The corollary implies that patients with low HbF levels should have more severe clinical courses. We investigated this in a retrospective study of 50 Jamaican patients with steady-state HbF levels below 1% compared with a control group (A) of 54 subjects with steady-state HbF levels between 2.5 and 3.4% (around the 25th centile for our population), and a second control group (B) of 60 patients with steady-state HbF levels between 4.6 and 5.2% (around the 50th centile). Comparisons across the groups indicated significantly fewer females in the study group (16, 50 and 57%, respectively). Examination for haematological trends across the groups showed positive linear trends for haemoglobin (Hb) (P=0.004), packed cell volume (PCV) (P=0.01), mean cell volume (MCV) (P= < 0.001), mean cell haemoglobin (MCH) (P= < 0.001) and a negative trend for haemoglobin A2 (P=0.03). Clinically, there were no differences in the incidence of painful crises, abdominal crises and the acute chest syndrome, but leg ulcers were significantly less frequent in the study group (P=0.04). Therefore low HbF levels do not appear to increase the clinical severity of SS disease and may be protective against leg ulceration.