Overweight, insulin resistance and blood pressure (parameters of the metabolic syndrome) in uric acid urolithiasis

Overweight, arterial hypertension and disturbances of the carbohydrate metabolism are important parameters of the metabolic syndrome (MS). The most important factor regarding renal pathophysiology is insulin resistance resulting in alterations of urine acidification and low urine pH. Since low urine pH is the main risk factor for uric acid urolithiasis (UAU), UAU may be regarded as a renal manifestation of the MS. So far, there are only few data on the prevalence of parameters of the MS in UAU patients especially with regard to the severity of the disease and recurrence rate, respectively. The objective of this study was to know more about the prevalence of different parameters of the MS and their importance for the natural history of this type of renal stone disease using a total number of 167 consecutive patients with pure UA stones. Stone analysis was performed by polarization microscopy and X-ray diffraction. The following parameters were measured: age, sex, systolic and diastolic arterial blood pressure (RRs and RRd), number of stone episodes, diabetes mellitus (DM); serum: creatinine, calcium, sodium, potassium, uric acid, glucose; urine: pH-profiles, citrate, calcium, uric acid, ammonia, urea, and creatinine. The following results were obtained (means ± standard deviations): age 61 ± 13 years, BMI 30 ± 6 kg/m², BP 147/84 ± 22/13 mmHg, number of stone episodes 1.8 ± 1.2, DM 32%; serum: creatinine 1.3 ± 0.6 mg/dl, glucose 136 ± 52 mg/dl, UA 6.3 ± 1.8 mg/dl, calcium 2.4 ± 1.3 mmol/l, sodium 134 ± 18 mmol/l, potassium 4.1 ± 0.4 mmol/l; urine: pH 5.87 ± 0.27, volume 2.4 ± 1.1 l/d, calcium 3.5 ± 2.5 mmol/d, UA 3.9 ± 2.4 mmol/d, citrate 1.3 ± 1.1 mmol/d, ammonia 41 ± 26 mmol/d, urea 390 ± 176 mmol/d. A significant positive correlation could be found for BMI and urea excretion, BMI correlated negatively with RRs and RRd. There was no significant correlation between BMI, urine pH, citrate, ammonia and UA in serum and urine. Undue acidity and hyperuricosuria were found in two-thirds of the UAU patients, increased urea excretion and decreased excretion of ammonia in less than 25%, Hyperuricemia in 37%. There was no significant correlation between the number of stone episodes and any other parameter studied. Overweight, arterial hypertension and DM as parameters of the MS are frequent in many patients with UAU. However, these parameters do explain the pathogenesis in two-thirds of the patients. The severity of the disease and the recurrence are not influenced by the presence of these metabolic parameters. Therefore, MS is no prognostic factor in UAU.