Renal clearance of cystathionine in homozygous and heterozygous cystathioninuria, cystinuria, and the normal state.

Cystathionine is more readily cleared from the plasma than other amino acids. This is because the amino acid has a very low tubular maximum (Tm), in the order of 1 mumole per minute per 1.73 square meters body surface area (BSA). No essential differences in the reabsorption of cystathionine were observed in four normal subjects, two patients with homozygous cystathioninuria, one patient with heterozygous cystathioninuria, and one patient with cystinuria. Apparent net tubular secretion of cystathionine was demonstrated in a child with homozygous cystathioninuria only after an intravenously administered load of lysine.