To survey the urinary risk factors associated with recurrent
calcium stone and the contribution of
renal tubular acidosis to the prevalence of recurrent
calcium stone formation in Thai recurrent stone formers.
MATERIAL AND METHOD: There were 86 consecutive recurrent
calcium stone formers. Three-day dietary record, serum biochemical parameters, first morning urine pH, and two 24-hour urine collections were obtainedfrom each subject. Urinary risk factors for
calcium stone formation were determined from the average of the 2-day urine collection. Normal controls were 34 subjects matched for aged, sex, and weight, and without a history of renal stone formation.
RESULTS: Seven patients (8.1%) were diagnosed as incomplete
renal tubular acidosis (iRTA). Among the 79 idiopathic
calcium stone formers (ISF), 69.6%, 15.2%, 10.1%, 7.2% and 1.3% of patients were hypocitraturia,
hypercalciuria, low urinary volume, hyperuricosuria and
hyperoxaluria, respectively. The common combinations of risk factors were hypocitraturia plus low urine output (8.9%) or plus
hypercalciuria (7.6%). There were significant differences between ISF and normal controls in urinary
oxalate excretion (0.16 +/- 0.01 vs 0.12 +/- 0.01, p < 0.05), urinary
calcium/citrate ratio (4.49 +/- 0.50 vs 2.83 +/- 0.34, p < 0.01) and ion activity product for
calcium oxalate stone (0. 46 +/- 0.03 vs 0. 33 +/- 0.03, p < 0. 05). Urinary
citrate in ISF varied directly with net alkaline absorption (r = 0.34, p < 0.005) and urinary
potassium (r = 0.54, p < 0.001). There were significant correlations between urinary
calcium excretion and both
sodium excretion (r = 0.42, p < 0.001) and
urea excretion (r = 0.41, p < 0.001) in ISE There were seven (8.1%) with incomplete
renal tubular acidosis. Patients with iRTA tended to have less urinary
citrate and higher
calcium/citrate ratio than did ISF, but
hypercalciuria was uncommon.
CONCLUSIONS: Hypocitraturia was the most common urinary risk factor found in Thai recurrent idiopathic
calcium stone formers followed by
hypercalciuria and low urinary volume. Almost one-fourth of the stone formers had multiple risk factors. Hypocitraturia might result from low
potassium and low alkaline intake. iRTA was common among recurrent
calcium stone formers. Determination of morning urine pH should be a part of the investigations for urinary risk factors to avoid overlooking the diagnosis of iRTA.