By age 70, 11% of men and 6% of women in the United States will have had at least one occurrence of kidney stones (nephrolithiasis).1,2 This translates to a nationwide incidence rate of one in 11. More than 50% of those affected by kidney stones will experience a recurrence.3
Treatments for kidney stones, though available, are underutilized; only 3% of patients are treated after their first occurrence.3 Since treatment depends on the composition of the initial stone, identification is essential. Once the stone type is identified, treatment can be directed at the metabolic abnormality that caused the stone’s formation.
There are five types of stones: calcium-based, struvite, uric-acid, cystine, and the problematic “mixed.” The most common is the calcium-based stone, which accounts for nearly 80% of identified stones.3,4 It is not the amount of calcium in the diet that usually causes a stone but rather the calcium excreted by the kidney collecting system.
One of the first recommendations for treatment of a calcium-based stone is a low-salt diet.4 Extra urinary sodium excretion (as a result of excess consumption) will increase calcium excretion in the urine. Decreasing salt in the diet will reduce sodium in the urine and, by extension, calcium as well. If conservative dietary changes are insufficient, a thiazide diuretic may be prescribed. (At present, a randomized clinical trial assessing treatment with oral potassium vs thiazides vs allopurinol for calcium-based stones is underway. Data from this trial will direct prevention strategies for calcium-based stones in the future.)
Uric acid stones can occur if the urine contains a high level of purine as a result of acidic foods in the diet. This usually means a diet rich in meats, shellfish, and high-purine foods (the same ones that can trigger gout).5 Control of the diet, alkalization of the urine, and/or treatment of the underlying high serum uric acid levels with allopurinol are the current recommended treatments.6
Struvite stones are caused by kidney infections. Many require long-term low-dose antibiotics in order to reduce reoccurrence.6 It is vital to know if a stone is struvite, since the treatment is significantly different from that for other types of stones.
Cystine stones result from a genetic disorder (cystinuria) that affects an amino acid. Often, these types of stones are seen in younger patients, and any teen who presents with kidney stones should undergo a work-up for the genetic abnormality. (See Zuber K. Woman, 26, with kidney stones. Clinician Reviews. 2011;21(3):8-10.)
When a patient complains of severe, colicky abdominal pain, hematuria, or a sharp pain in the back or flank, the thought of kidney stones must be front and center. Evaluation incudes both serum testing and CT.5,7 Abdominal plain films and/or an intravenous pyelogram were considered state of the art in the 1980s and 1990s, but helical CT has become the scan of choice since it allows for measurement of the size, position, and level of obstruction. Helical CTs are increasingly available nationwide—and a sensitivity of 95% to 100% makes them the preferred method of evalution.5,8
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. Worcester EM, Coe FL. Calcium kidney stones. N Engl J Med. 2010;363:954-963.
3. Rule A, 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. Diet and kidney stones. www.kidney.org/atoz/content/diet.cfm. Accessed September 9, 2104.
5. Jackman SV, Potter SR, Regan F, Jarrett TW. Plain abdominal x-ray versus computerized tomography screening: sensitivity for stone localization after nonenhanced spiral computerized tomography. J Urol. 2000;164(2):308-310.
6. Lipkin ME, Preminger GM. Demystifying the medical management of nephrolithiasis. Rev Urol. 2011;13(1):34-38.
7. National Institute of Diabetes and Digestive and Kidney Diseases. Kidney stones in adults: what are the types of kidney stones? http://kidney.niddk.nih.gov/KUDiseases/pubs/stonesadults/index.aspx#types. Accessed September 9, 2014.
8. Harrington K, Torreggiani W. CT analysis of renal stone composition: a novel and noninvasive method to analyse stones. Ir Med J. 2014;107(3):69.