Each year in the United States alone, more than half a million patients are seen in emergency departments with kidney stones. This translates to a stone incidence of 9% of all males and 6% of all females over the lifespan, or 1 in 11 people.1 Of these, 53% will have another stone during their lifetime.2 Since kidney stones are extremely painful and can cause permanent kidney damage, the ability to predict which patients are likely to have a stone recurrence is extremely valuable. Recently, an online calculator has been developed that can help clinicians predict which first-time kidney stone patients are in the “worrisome” group and which are less likely to have a recurrence.3
Kidney stones (nephrolithiasis) are increasingly common in males, those between ages 30 and 50, and those with certain underlying medical conditions, such as hypertension, diabetes, and gout, as well as those with a history of bariatric surgery.4 A family history of stone formation is also predictive.
Since more than half of patients will have a second episode of kidney stones, the ability to identify and aggressively treat at-risk patients is vital. Using a data set of clinical characteristics from more than 2,000 first-time kidney stone patients from Olmsted County, Minnesota, and following these patients longitudinally for more than 20 years, Rule et al identified patients who had a second episode of kidney stones—as well as the characteristics associated with stone recurrence.5 They then developed a multivariate calculator, the ROKS nomogram, which can be used after a patient’s first episode of kidney stones to predict the likelihood of stone recurrence at 2, 5, and 10 years.3 The authors of the ROKS stone calculator were inspired by the World Health Organization’s FRAX calculator, which predicts 10-year fracture probability.5,6
Rule et al identified 11 risk factors that they incorporated into the ROKS calculator. These include, but are not limited to, age, sex, race, family history, hematuria, presence of uric acid stones, and characteristics of the position of the initial stone in the pelvis. Not surprisingly, Rule et al found the kidney stone recurrence rate greatest in younger males who were white and had a family history of stones.
Minnesota, it should be noted, is an area of the country where summers are cooler; since people in warmer climates are at increased risk for kidney stones (particularly during the summer months), it is possible that the ROKS calculator would be even more useful in the South or Southwest than in the original study setting.5
A free, downloadable app of the ROKS calculator is available at the QxMD app “Calculate” (iOS: http://qx.md/qx, Android: http://qx.md/android, or web-based http://qxmd.com/ROKS).
Any episode of kidney stones increases the risk for chronic kidney disease and/or kidney failure.7 The absolute risk increase, though small, is present; any preventive measures one can offer at-risk patients is valuable. These range from increasing fluids and acidifying the urine to adding medications, including thiazide diuretics and allopurinol, to reduce stone formation. Unfortunately, only 3% of all first-time kidney stone patients are currently treated with medication to prevent a second episode.3 This creates an unnecessary risk for complications in a significant number of patients. By identifying members of the stone population who are likely to have a second event, clinicians can reduce the risk for recurrence.
Close monitoring of a patient with a significant stone history is vital. The ROKS calculator will allow practitioners to identify patients at increased risk for recurrent kidney stones and treat them aggressively—reducing the associated kidney damage and pain.
References
1. Scales CD Jr, Smith AC, Hanley JM, Saigal CS. Urologic Diseases in America Project: prevalence of kidney stones in the United States. Eur Urol. 2012;62:160-165.
2. Ljunghall S. Incidence of upper urinary tract stones. Miner Electrolyte Metab. 1987;13(4):220-227.
3. Rule AD, Lieske JC, Li X, et al. The ROKS Nomogram for Predicting a Second Symptomatic Stone Episode. J Am Soc Nephrol. 2014 Aug 7. [Epub ahead of print]
4. National Kidney Foundation. Kidney stones: how common are kidney stones? www.kidney.org/atoz/content/kidneystones.cfm. Accessed September 24, 2014.
5. Eisner BH, Goldfarb DS. A Nomogram for the Prediction of Kidney Stone Recurrence. J Am Soc Nephrol. 2014 Aug 7. [Epub ahead of print]
6. Kanis JA on behalf of the World Health Organization Scientific Group (2007). Assessment of osteoporosis at the primary healthcare level: report of a WHO Scientific Group. www.iofbonehealth.org/sites/default/files/WHO_Technical_Report-2007.pdf. Accessed September 26, 2014.
7. Alexander RT, Hemmelgarn BR, Wiebe N, et al. Kidney stones and kidney function loss: a cohort study. BMJ. 2012;345:e5287.