Statins may protect against urinary stones

Key Points

San Diego-Statin use in patients with hyperlipidemia appears to protect against urinary stone formation, findings from a retrospective review of military electronic medical records indicate.

"Patients with a cholesterol disorder taking a statin medication were half as likely as patients not taking a statin to develop a stone," reported first author James Masterson, MD, a fourth-year urology resident at the Naval Medical Center, San Diego.

The finding lends further support to the hypothesis first proposed by Marshall L. Stoller, MD, et al in 2004 that the pathogenesis of urinary stone formation may be vascular in nature (J Urol 2004; 171:1920-4). Dr. Stoller, professor and vice chair of urology at the University of California, San Francisco, was also senior author of the current study.

"We know that statins reduce cholesterol and cholesterol allows calcification within the vasa recta, so we hypothesized that statins might reduce stone formation," said Dr. Masterson, who presented the findings at the AUA annual meeting in Washington.

The Armed Forces Health Longitudinal Technology Application of the Southwestern United States region database, an electronic medical record for retired and active duty military personnel and their families, served as the source for the analysis. The database was searched for ICD-9 codes and date of diagnosis of a lipid metabolism disorder, the presence of renal or ureteral calculus, and initial prescription for statin medication. The query identified 57,326 patients with hyperlipidemia, 6,313 as having urolithiasis, and 1,998 with both a lipid metabolism disorder and urinary stones.

Those with a lipid metabolism disorder were older and more likely to be male, obese, have hypertension, have diabetes mellitus, have coronary heart disease, have ischemic heart disease, and use tobacco.

Some 1,030 of 32,386 patients on a statin developed a stone (3.2%) compared with 968 of 24,940 who were not on a statin (3.9%), yielding an odds ratio (OR) for stone formation of 0.813 in statin users on univariate analysis.

The relationship was more profound on multivariate analysis: The adjusted OR for stone formation among statin users was 0.50 overall (p<.001), 0.585 for men (p<.001), and 0.363 for women (p<.001). Congruent with previous findings, hypertension and obesity each increased the odds for stone formation (OR: 1.749 and 1.534, respectively; p<.001 for each).

In that urinary stones may be the first symptom of a metabolic syndrome, the new research suggests that ordering a lipid panel when doing a stone workup may be prudent, Dr. Masterson said.

"We've never seen anything that has reduced stone formation by 50%," Dr. Stoller told Urology Times. "We should be looking at the vasculature to understand the initial stone-forming event."

"If anything, the statin group should have had an even higher risk of stones because they were more obese and more had metabolic syndrome," added Dr. Masterson.

Epidemiologic evidence also supports a vascular etiology of urinary stones, said Dr. Stoller, as nephrolithiasis has been linked to an increased prevalence of myocardial infarction, cardiac angina, congestive heart failure, and coronary artery calcification.