Staghorn calculi composition frequently metabolic

Chicago-Among patients with staghorn calculi, researchers have discovered a shift in the composition of these stones, with metabolic stones becoming more prominent.

Researchers from Vanderbilt University, Nashville, TN, reported retrospective data from 47 patients (51 kidneys) who underwent percutaneous nephrolithotomy for complete staghorn calculi (defined as a radiographic stone in the renal pelvis and all calyces) between April 2005 and March 2010. Stone analysis showed that 29 (57%) of the 51 complete staghorn calculi were metabolic stones, while only 22 (43%) were struvite. Among patients found to have a metabolic stone, all 14 who consented to a metabolic analysis were found to have multiple metabolic abnormalities.

Findings differ from AUA guidelines

The findings also differed from information in the AUA guidelines that suggest metabolic staghorn calculi are most often cystine or uric acid and only rarely calcium oxalate or phosphate. Among the metabolic stones, calcium phosphate (predominantly hydroxyapatite) represented the most common type (55%), followed by uric acid (21%), calcium oxalate (14%), and cystine (10%). There were no significant differences between patients with metabolic versus struvite stones with respect to age, side of involved kidney, body mass index, American Society of Anesthesiologists classification, or stone area, and postoperative outcomes were similar for patients with metabolic and struvite stones.

However, compared with patients having struvite stones, those with metabolic stones were about three times more likely to be male (55% vs. 18%) and about twice as likely to have a negative preoperative urinary culture (68% vs. 38%). In patients with stone culture data, negative results were similarly more likely in patients with metabolic stones.

"A relatively recent study involving a Japanese population of patients with staghorn calculi also found a predominance of metabolic stones, and the researchers suggested a lower rate of urinary infections in Asian cultures might account for the finding. Although we also saw a decreased rate of infection in our patients with metabolic versus struvite calculi, we are not certain that explanation is relevant to our population," Dr. Viprakasit told Urology Times.

Dr. Viprakasit speculated that practice patterns such as routine stone analysis or worsening dietary and lifestyle practices may provide a partial explanation for the higher incidence of metabolic stones.

"Our findings have definitely confirmed for our group the importance of aggressive medical management, counseling, and routine evaluation in our active metabolic stone patients to prevent the potential development of staghorn calculi," he said.