Nonphysiological anaemia of prematurity.

Clinical and haematological findings at the nadir of the refractory, early anaemia of prematurity were compared in a study of 95 preterm infants. 53% of 30 babies less than 32 weeks' gestational age at birth had abnormal clinical features resulting from anaemia at its nadir, with a combination of tachycardia, tachypnoea, dyspnoea and feeding difficulties, diminished activity, and pallor. The expression 'available oxygen', derived from the Hb concentration and Hb-O2 affinity, correlated more closely with clinical features of anaemia that did the Hb concentration alone. A formula is presented that predicts the 'available oxygen', provided the Hb concentration and post-conceptual age are known; this avoids the need for direct measurement of Hb-O2 affinity. Clinical anaemia is common in preterm infants with Hb concentrations of up to 10.5 g/dl, consequent on the high O2 affinity of fetal Hb. This is the first description of any common clinical consequence of high Hb-O2 affinity.