Blood Volume and Bilirubin Production in Acute Intermittent Porphyria

Mean blood volume in 13 patients with acute intermittent porphyria was 80 per cent of normal (p less than 0.01). There was a parallel reduction in both plasma and total red-cell volumes. In seven patients the half-life of 51Cr-labeled red cells ranged from 24 to 32 days. The finding of a reduced red-cell volume without accelerated red-cell destruction indicated that effective erythropoiesis was reduced. Ferrokinetic studies in one patient also demonstrated decreased erythropoiesis (plasma iron turnover was 70 per cent of normal). The bilirubin production rate in six patients was proportional to the circulating red-cell mass (r = 0.84), indicating that there was no increase in the early labeled fraction of bilirubin. In one patient a normal estimate for this fraction was found with the use of glycine-2–14C. These results indicate that ineffective erythropoiesis is not increased in acute intermittent porphyria and also suggest that there is no marked increase in hepatic bilirubin production.