METABOLIC ABNORMALITIES PREDISPOSING TO C ALCULUS FORMATION IN RENAL-TRANSPLANT PATIENTS

Urolithiasis after renal transplantation is uncommon. However, little is known about what factors could influence this low incidence of ston e formation, despite these patients being potentially exposed to a hig h prevalence of metabolic abnormalities predisposing calculus formatio n. In order to assess the prevalence of these metabolic abnormalities, we surveyed 133 unselected renal transplant patients in a cross-secti onal study. The following were measured: serum creatinine, calcium, ph osphorus, uric acid, magnesium bicarbonate, PTH, as well as the 24 h u rinary excretion of calcium, phosphorus, uric acid, citrate, oxalate a nd magnesium. Hypercalciuria was observed in 17 patients (13%), hiperu ricosuria in 8 (6%), hyperoxaluria in 30 (22%), hypocitraturia in 102 (77%) and hypomagnesiuria in 15 (11%). Among patients with normal rena l function (Cr < 2 mg/dl (N = 105 patients) the prevalence of metaboli c abnormalities were similar to the whole group. The mean 24 h urinary output was high (2.239 +/- 684 ml). Patients with hypocitraturia show ed lower serum bicarbonate concentrations (25.3 +/- 2.1 vs 26.6 +/- 1. 6 mmol/l, p = 0.01). Hyperparathyroidism among patients with normal re nal function was not associated with a higher prevalence of urinary ex cretion abnormalities. Only 5 patients (4%) developed urolithiasis aft er transplantation. In one patient no metabolic abnormalities could be demonstrated. The rest of these patients showed two or three associat ed metabolic abnormalities (hypocitraturia, hypomagnesiuria, hyperoxal uria or hypercalciuria). In conclusion, metabolic abnormalities predis posing urolithiasis after renal transplantation are highly prevalent. Hypocitraturia is the most common abnormality and its etiology may be related to acidosis. High urinary output and the lack of oversaturatio n in urine may prefect these patients from a higher incidence of calcu lus formation.