Metabolic investigation of recurrent nephrolithiasis: compliance with recommendations

OBJECTIVES: Nephrolithiasis is a recurrent condition with significant associated morbidity and economic impact. Although urologic intervention addresses symptomatic stone episodes, prevention of recurrences with proven medical therapy is indicated. METHODS: This retrospective study examined 97 patients who presented in 1997 and 1998 with recurrent nephrolithiasis in a large tertiary care center for the presence of an appropriate metabolic investigation as recommended by the National Institutes of Health Consensus Conference. Complete data were abstracted from the hospital and private clinic charts. RESULTS: The average patient age was 50.5 years; 61.9% of patients were men. The mean number of stones per patient was 5.6 (range 2 to 62), with stone analysis performed for 78 patients. Fifty-eight stones (74.4%) were calcium oxalate and/or phosphate, 14 (17.9%) urate, 8 (10.3%) struvite, and 3 (3.8%) cystine. Five patients had two stone types on different occasions. Either lithotripsy or a urologic procedure was required for at least one stone presentation in 89 patients (91.8%). An investigation for stone disease was pending in 54 patients (55.7%). A complete evaluation, satisfying the preset criteria, was performed in 34 patients (35.1%). Six patients who did not undergo evaluation were lost to follow-up. Univariate analysis revealed that referral to a nephrologist (P = 0.001), treatment with medications used for stone disease (P = 0.008), and urate stones (P = 0.005) were associated with a complete investigation. Similarly, these were independently associated with a complete evaluation in regression analysis of 77 complete data sets, with odds ratios of 24.4 (nephrology referral), 4.9 (medication use), and 5.6 (urate stones). CONCLUSIONS: The results of this study demonstrate that a significant proportion of patients with recurrent nephrolithiasis do not undergo appropriate metabolic investigations. Efforts should be made to improve the evaluation of these patients.