Urea kinetics in adults with homozygous sickle cell disease

The kinetics of urea metabolism were measured in four adults with homozygous sickle cell disease (HbSS). On a dietary intake of 1.2 to 2.7 g protein/kg/d the rate of urea production was 188 to 277 mg nitrogen/kg/d. A relatively small proportion of the urea was excreted in the urine (40 per cent), with a high fixed rate of hydrolysis in the bowel, 145 mg nitrogen/kg/d. Although 50 per cent of the nitrogen from hydrolysed urea was resynthesized to urea, and a further 10 per cent may have been lost in the stool, it is estimated that 58 mg nitrogen/kg/d was available for synthetic metabolic activity. Urea kinetics in sickle cell disease subjects are markedly different from normals, and this may be a reflection of the metabolic demands for increased red cell synthesis.