The purpose of the present study was to compare the clinical characteristics of "pure" uric acid (UA) stone formers with that of "pure" calcium oxalate (CaOx) stone formers and to determine whether renal handling of UA, urinary pH, and urinary excretion of promoters and inhibitors of stone formation were different between the two groups. Study subjects comprised 59 patients identified by records of stone analysis: 30 of them had "pure" UA stones and 29 had "pure" CaOx nephrolithiasis. Both groups underwent full outpatient evaluation of stone risk analysis that included renal handling of UA and urinary pH. Compared to CaOx stone formers, UA stone formers were older (53.3 +/- 11.8 years vs. 44.5 +/- 10.0 years; P = 0.003); they had higher mean weight (88.6 +/- 12.5 kg vs. 78.0 +/- 11.0 kg; P = 0.001) and body mass index (29.5 +/- 4.2 kg/m(2) vs. 26.3 +/- 3.5 kg/m(2); P = 0.002) with a greater proportion of obese subjects (43.3% vs. 16.1%; P = 0.01). Patients with "pure" UA lithiasis had significantly lower UA clearance, UA fractional excretion, and UA/creatinine ratio, with significantly higher serum UA. The mean urinary pH was significantly lower in UA stone formers compared to CaOx stone formers (5.17 +/- 0.20 vs. 5.93 +/- 0.42; P < 0.0001). Patients with CaOx stones were a decade younger, having higher 24-h urinary calcium excretion (218.5 +/- 56.3 mg/24 h vs. 181.3 +/- 57.1 mg/24 h; P = 0.01) and a higher activity product index for CaOx [AP (CaOx) index]. Overweight/obesity and older age associated with low urine pH were the principal characteristic of "pure" UA stone formers. Impairment in urate excretion associated with increased serum UA was also another characteristic of UA stone formers that resembles patients with primary gout. Patients with pure CaOx stones were younger; they had a low proportion of obese subjects, a higher urinary calcium excretion, and a higher AP index for CaOx.

Urolithiasis is the third most common pathological disease afflicting the urinary tract, and usually occurs between the third and fourth decades of an individual's life. Epidemiological studies about this condition are lacking in our country. In 1998, we performed an epidemiological, cross-sectional study of the prevalence of urolithiasis in a sample of 1,086 subjects, which included men and women of all ages, selected from the general population of the city of Buenos Aires. The method used to gather basic information was an auto administered questionnaire about the present or past history of urolithiasis that was handled at the dwelling by a trained volunteer. We found a 3.96% lifetime prevalence of urolithiasis in the general population of Buenos Aires. The rate was slightly higher in men (4.35%) than in women (3.62%), with a male to female ratio of 1.19:1. No case of urolithiasis was found in subjects under the age of 20. In subjects over 19 years, the prevalence rate of the disease was 5.14%; 5.98% for men (CI 3.41-8.55%) and 4.49% for women (CI 2.61-6.37%). Prevalence increased with age, ranging from 2.75% in the 20-39 age group to 7.79% in those >or=60 years. The life time prevalence rate of urolithiasis observed in Buenos Aires is similar to that reported in a few other studies performed among males and females in the general population of USA and Europe. Prevalence of urolithiasis increases with age both in men and in women.

Although urine phosphate loss has been associated with hypercalciuria, it is debated how frequently renal phosphate leak is present in hypercalciuric patients. We reviewed the records of 100 consecutive adult patients who were diagnosed with idiopathic hypercalciuria and calcium urolithiasis, searching for the presence of renal phosphate leak. The renal phosphate threshold, normalized for the glomerular filtration rate (TmPO4/GFR), of the hypercalciuric patients followed a normal distribution and had a good correlation with serum phosphate ( r=0.77; p<0.0001). There were no correlations between TmPO4/GFR and urinary calcium or between serum phosphorus and urinary calcium. We found only nine patients (9%) with renal phosphate leak. These patients had a mean TmPO4/GFR of 2.19 mg% (0.70 mmol/l) and serum phosphorus of 2.65 mg% (0.85 mmol/l). Nevertheless, urinary calcium was not significantly different between patients with or without low TmPO4/GFR. We conclude that renal phosphate leak is an infrequent finding in patients with idiopathic hypercalciuria and is not associated with a higher urinary calcium loss.

Pamidronate administered IV was well tolerated when used for treating osteoporosis or other metabolic osteopathies in our study population. The clinical AEs observed with IV pamidronate administration were not serious and hematologic changes were mild, transient, and not associated with dose, time of treatment, or any particular underlying disease. An increase in sCreat level was the most frequent biochemical complication and was found in patients with additional risk factors for renal failure and particular diseases. Whether certain patients with risk factors for osteoporosis may require even fewer IV administrations of the drug is an issue that remains to be elucidated.

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