Renal tubular acidosis in recurrent renal stone formers

Renal tubular acidosis (RTA) is a well-known metabolic disturbance that may promote recurrent renal stone formation. However, its incidence, screening criteria and association with other lithogenic metabolic abnormalities are not established in recurrent nephrolithiasis. 10 of 50 consecutive recurrent renal stone formers had a persistent fasting morning urinary pH above 6.0 and/or a basal plasma bicarbonate concentration below 20.0 mM. Acid and alkaline loads disclosed RTA in 3 patients: 1 patient had incomplete type-1 distal RTA in addition to hyperoxaluria; a second patient showed complete type-2 proximal RTA, hyperoxaluria and renal hypercaliuria; and a third patient had incomplete proximal RTA without any other metabolic derangement. These results reinforce the importance of RTA as an isolated metabolic abnormality among recurrent renal stone formers. In addition, RTA appears to be more commonly associated with other lithogenic metabolic derangements than has been previously suspected. The extensive metabolic protocol used in this study provides a useful tool in the diagnosis and therapeutic considerations of recurrent nephrolithiasis.