Background: Cross-sectional studies have shown that nephrolithiasis is more frequently found in hypertensive patients than in normotensive subjects, but the pathogenic link between hypertension and stone disease is still not clear.
Methods: Between 1984 and 1991, we studied the baseline stone risk profile, including supersaturation of lithogenic salts, in 132 patients with stable essential hypertension (diastolic blood pressure of more than 95 mm Hg) without stone disease and 135 normotensive subjects (diastolic blood pressure less than 85 mm Hg) without stone disease who were matched for age and sex (controls). Subsequently, both controls and hypertensives were followed up for at least five years to check on the eventual formation of kidney stones.
Results: Baseline urine levels in hypertensive males were different from that of normotensive males with regards to calcium (263 vs. 199 mg/day), magnesium (100 vs. 85 mg/day), uric acid (707 vs. 586 mg/day), and oxalate (34.8 vs. 26.5 mg/day). Moreover, the urine of hypertensive males was more supersaturated for calcium oxalate (8.9 vs. 6.1) and calcium phosphate (1.39 vs. 0.74). Baseline urine levels in hypertensive females were different from that of normotensive females with regards to calcium (212 vs. 154 mg/day), phosphorus (696 vs. 614 mg/day), and oxalate (26.2 vs. 21.7 mg/day), and the urine of hypertensive females was more supersaturated for calcium oxalate (7.1 vs. 4.8). These urinary alterations were only partially dependent on the greater body mass index in hypertensive patients. During the follow-up, 19 out of 132 hypertensive patients and 4 out of 135 normotensive patients had stone episodes (14.3 vs. 2.9%, chi-square 11.07, P = 0.001; odds ratio 5.5, 95% CI, 1.82 to 16.66). Of the 19 stone-former hypertensive patients, 12 formed calcium calculi, 5 formed uric acid calculi, and 2 formed nondetermined calculi. Of the urinary factors for lithogenous risk, those with the greatest predictive value were supersaturation of calcium oxalate for calcium calculi and uric acid supersaturation for uric acid calculi.
Conclusions: A significant percentage of hypertensive subjects has a greater risk of renal stone formation, especially when hypertension is associated with excessive body weight. Higher oxaluria and calciuria as well as supersaturation of calcium oxalate and uric acid appear to be the most important factors. Excessive weight and consumption of salt and animal proteins may also play an important role.