Prevention and Treatment of Kidney Stones

Basic definition and introduction to kidney stones:

Kidney stones, also called renal calculi or nephrolithiasis, form as crystalline aggregations of minerals in the urine. The majority of kidney stones (80%) contain calcium, of which calcium oxalate stones are by far most common, followed by calcium phosphate and mixed calcium phosphate/oxalate. Other common stones include struvite stones (10%, comprised of magnesium, ammonium, phosphate and caused by urease-producing bacteria such as Proteus or Klebsiella), uric acid stones (10%, mostly uric acid, but also uric acid and calcium mixtures), and cystine stones (1%). In general, kidney stones had a recurrence rate of 50% within the first 10 years, and 80% in the next 20-30 years. In situations of recurrent stones, it is important to rule out underlying diseases, such as hyperparathyroidism, sarcoidosis, and renal tubular acidosis that may be causing the stone formation.

Relevance to primary care:

Kidney stones are a common disease in the primary care setting and can occur in up to 15% of men and 7% of women in the United States. Primary care physicians can cost-effectively prevent and treat recurrent kidney stones rather than having specialists treat uncomplicated cases. In one study, the authors found an average savings of over $2000 per patient with medical prevention/treatment of recurrent stones and avoidance of urologic procedures and hospitalization. Evaluation of an initial episode can also be easily accomplished in a primary care setting. Initial screening should include complete history (focusing on such medications, family history of stones or kidney diseases, IBD, and dietary intake of protein, purines, uric acid, sodium, fluids, oxalate) and physical. Relevant initial labs include complete chemistry panel, uric acid, phosphate, urinanalysis, urine culture if indicated. Radiographic evaluation by plain films, intravenous pyelography, or helical CT should also be done. Stone analysis is fairly inexpensive (costing $20-30) and should be considered. Additional screening including 24 hour urine collection and analysis should be considered for recurrent stone formers and any child former. Risk factors for stones are summarized in a table below.

When to refer to a urologist?

It is important to identify when patients initially present who needs emergent urologic evaluation. Patients who appear infected in the setting of an obstructing stone, are anuric, or have acute renal failure secondary to bilateral obstruction require emergent evaluation. In addition, patients with intractable nausea/vomiting, refractory pain, or poor general medical status may require additional evaluation and hospitalization. Another indication for referral is failure of medical therapy requiring surgical treatment, including extracorporeal shock-wave lithotripsy, percutaneous ultrasonic lithotripsy, ureteroscopic lithotripsy or removal.

Prevention and treatment in the primary care setting:

Most stones (80%) causing renal colic will pass spontaneously. As such, most patients can be treated with oral analgesics and increased fluid intake as an outpatient in the acute setting. After the acute setting has passed, prevention and treatment of recurrent stones may be achieved in several ways:

• Increased fluid intake: recommended intake of eight 8-oz glasses of water per day, including one glass right at bedtime or adequate enough hydration to produce at least 2 L of urine daily

• Dietary changes to reduce intake of salt, protein (a source of purines, which a precursor to uric acid), refined sugars, and oxalate (see table below for brief list of foods high in oxalate).

• Citrate supplementation has been shown to be helpful in preventing stones. Roughly 60-80 mEq of potassium citrate daily is an effective dose, although some studies have shown that as little as 20 mEq daily is helpful. Certain high citrate containing foods such as lemon juice and orange juice may also be somewhat helpful. Magnesium supplementation has also been shown to decrease stone formation.

• Calcium should not be limited as studies have shown that decreased calcium intake has no effect on stone formation, but does negatively effect bone density. To prevent osteoporosis, calcium intake should be maintained and even supplemented when indicated.

• Pharmacologic treatment recommendations may vary depending on the stone type. For calcium stones, treatment with thiazides has been shown to decrease Ca urinary excretion and thus stone formation. Allopurinol may be used in situations with uric acid stones and hyperuricosuria, although first line therapy is still potassium citrate.

References:

Parks JH, Coe FL. The financial effects of kidney stone prevention. Kidney Int 1996;50:1706-12.

Pak CY, Fuller C, Sakhaee K, Preminger GM, Britton F. Long-term treatment of calcium nephrolithiasis with potassium citrate. J Urol. 1985 Jul;134(1):11-9.

Goldfarb DS, Coe FL. Prevention of recurrent nephrolithiasis. Am Fam Physician. 1999 Nov 15;60(8):2269-76.

Wasserstein AG. Nephrolithiasis: acute management and prevention. Dis Mon. 1998 May;44(5):196-21

Parivar F, Low RK, Stoller ML. The influence of diet on urinary stone disease. J Urol. 1996 Feb;155(2):432-40.

Goroll and Mulley. Primary Care Medicine, 5^th edition. Lipincott Williams & Wilkins. Philadelphia, 2006. pg 897-901

Category: Surgery Notes