STONE DISEASE

Stone recurrence predictive score (SRPS) for patients with calcium oxalate stones
Lee Y, Huang W, Lu C, Tsai J, Huang J
Department of Surgery, Veterans General Hospital-Kaohsung, School of Medicine, National Yang Ming University, Taipei, Taiwan
J Urol. 2003; 170: 404-7

• Purpose: We developed a convenient, self-administered 8-item stone recurrence predictive score (SRPS) to predict the recurrence of calcium oxalate stones.
• Materials and Methods: An 8-item SRPS to predict stone recurrence was developed based on general patient data, including age, sex, urine volume, smoking, wine drinking, family history, stone number and history of gouty arthritis. Mean age of the 204 studied patients with calcium oxalate stones +/- SD was 59.4 +/- 14.5 years (range 24 to 83). The male-to-female ratio was 3:1. Of the patients 115 were recurrent stone formers and 89 were single stone formers. We compared all available general data in the recurrence and control groups.
• Results: Family history, stone number, gouty arthritis and SRPS were independent risk factors for stone recurrence. Mean SRPS in recurrent and single stone formers was 7.6 +/- 3.1 and 5.1 +/- 2.0, respectively (p = 0). An increase in SRPS had a significant positive correlation with stone recurrence (r2 = 0.859, p < 0.0001). At an SRPS cutoff of 7 or greater we achieved 61.7% sensitivity and 75.3% specificity to predict stone recurrence. At an SRPS of 11 or greater we found that 100% of patients had recurrent stones.
• Conclusions: With the introduction of the 8-item SRPS we provide a simple, convenient and reliable tool to predict calcium oxalate stone recurrence. Due to the characteristics of the high incidence of stone recurrence thorough metabolic evaluation may be justified in patients with an SRPS of 7 or greater and preventive measures are highly recommended in those with an SRPS of 11 or greater.
  
  
• Editorial Comment
  The efficacy of medical therapy in preventing stone recurrence has been established by several prospective, randomized trials. However, the cost-effectiveness of metabolic evaluation and medical therapy has been questioned, particularly for first-time stone formers. Lee and colleagues attempted to devise a stone recurrence predictive score (SRPS) based on an 8-item questionnaire relating to known stone risk factors that could stratify risk of stone recurrence and predict patients at high risk of recurrence. From a review of 204 patients followed for 2 to 5 years with radiographic studies and history, a linear regression model was constructed to determine the importance of each factor in predicting stone recurrence. The factors of positive family history, multiple stones, gouty arthritis and SRPS correlated with stone recurrence rate. At an SRPS cut-off level of ³ 7, the sensitivity and specificity of calcium oxalate stone recurrence is 62% and 75%, respectively.
  In this era of limited resources and costly medical care, stratification of risk is critical in order to allow identification of subgroups of patients more likely to suffer a defined event. Metabolic evaluation and indefinite medical therapy is costly. On the other hand, surgery is also costly, but the likelihood of experiencing a stone event requiring surgery is relatively low. As such, prophylactic treatment of patients after their first stone event may not be cost-effective. However if we can identify patients at highest risk of stone recurrence, medical evaluation and treatment in this group would avoid much suffering and expense and would likely justify the cost of treatment. This self-administered questionnaire provides a quick way to stratify patients, and although it will require further retrospective and prospective validation in larger patient groups, it represents a first step towards simple risk stratification.

Dr. Margaret S. Pearle
Associate Professor of Urology
University of Texas Southwestern Med Ctr
Dallas, Texas, USA