Amino-aciduria and enzymuria in patients with artificial heart valves

Fifteen patients with artificial heart valves and evidence of chronic intravascular haemolysis were studied for proximal tubular dysfunction. Three patients had haemosiderinuria and haemoglobinuria; 2 had haemoglobinuria alone. Increased urinary amino acid nitrogen occurred in 8, raised fractional beta 2-microglobulin excretion in 2, hypophosphataemia in 4, renal glycosuria in 1 and enhanced fractional urate excretion in 1. Urinary N-acetyl-beta-glucosaminidase (NAG) excretion increased in 7; the mean urinary NAG/creatinine ratio was raised to twice the upper limit of the normal range. Renal haemosiderosis due to chronic intravascular haemolysis could cause tubular injury.