Physiologic Implications of a Hemoglobin with Decreased Oxygen Affinity (Hemoglobin Seattle)

Abstract

Three patients heterozygous for hemoglobin Seattle were found to be anemic, with hematocrit levels of 24 to 33 per cent. Urinary erythropoietin excretion was 1 to 4 units per day. This low value suggested that an adequate oxygen supply had been achieved. Ferrokinetic studies showed a submaximal erythropoietic response to anemia. Oxygen equilibrium curves were constructed from data obtained on whole blood; oxygen tension at 50 per cent saturation was found to be 41 to 44 mm of mercury at 38°C and pH 7.4. This decreased oxygen affinity was shown by the study of isolated hemoglobin fractions to be due to the presence of hemoglobin Seattle. The increased availability of oxygen in these patients permits a normal tissue oxygen tension at a hemoglobin level lower than that in the normal person. Thus, patients with hemoglobin Seattle seem to have a normal oxygen supply, and an equivalent decrease in hemoglobin concentration may compensate for the decreased oxygen affinity of hemoglobin.