Studies on renal function in patients with cystinuria

Total and separate renal functions were evaluated in 40 patients with cystinuria. The average duration of the renal stone disease was 26 years (range 1-53). The patients had been subjected to a stone-preventing regimen composed of increased fluid intake, urinary alkalinization and treatment with a sulphydryl compound, tiopronin or D-penicillamine, for an average of 11.7 years (range 1-24). Urinary cystine concentration was determined regularly to monitor the treatment. All patients were examined with gamma camera renography and an assessment of glomerular filtration rate (GFR), and early and late renographic results could be compared in 30 patients. The early renographic evaluation showed that 43% of binephric patients (13/30) had an abnormal relative renal function (RRF) before the start of the stone-preventing treatment. At the late evaluation, 50% of binephric patients (17/34) had an abnormal RRF, while 30% of all patients (12/40) had a GFR below the age-related normal range. Thirty percent of 74 evaluated kidneys (22/74) had a separate GFR below an estimated age-related normal range. At the late evaluation only 30% of the patients had functionally unaffected kidneys with both normal GFR and bilateral normal renography. There was, however, no case with terminal renal failure. The separate GFR of kidneys with a history of staghorn stones was significantly lower than for kidneys without that special type of stones, but otherwise there was no relationship between renal functional impairment and other estimates of the activity of the renal stone disease. In conclusion, impairment of renal function is common in patients with stone-forming cystinuria. Stone-preventive treatment appears to be effective in preserving renal function. The high frequency of renal functional impairment justifies close surveillance of this group of patients. By renographic examination, unilateral changes in renal function can be detected at an early stage and patients at risk for further deterioration of renal function can be identified.