Kidney Stones

Posted by Graham McMahon • September 3rd, 2010

The latest article in our Clinical Practice series, Calcium Kidney Stones, comes to you from Drs. Elaine Worcester and Fredric Coe at the University of Chicago.

In the United States, the prevalence of kidney stones has risen over the past 30 years. By 70 years of age, 11.0% of men and 5.6% of women will have a symptomatic kidney stone. About 80% of stones are composed of calcium oxalate with variable amounts of calcium phosphate. Hospitalizations, surgery, and lost work time that are associated with kidney stones cost more than $5 billion annually in the United States.

Clinical Pearls

What is the approximate recurrence risk for patients with calcium stones?

After passage of a first stone, the risk of recurrence is 40% at 5 years and 75% at 20 years. Among patients with recurrent calcium stones who have served as control subjects in randomized, controlled trials of interventions, new stones formed in 43 to 80% of subjects within 3 years.

What is the most common metabolic abnormality in patients with recurrent calcium stones?

Hypercalciuria, the most common metabolic abnormality found in patients with recurrent calcium stones, is most often familial and idiopathic and is strongly influenced by diet.

Morning Report Questions

Q: How should symptomatic stones be managed?

A: Stones that have formed in kidneys do not require removal or fragmentation unless they cause obstruction, infection, serious bleeding, or persistent pain. Ureteral stones of less than 10 mm in diameter may be followed with conservative treatment in the absence of fever, infection, or renal failure, if pain is controlled. Opioid analgesics and nonsteroidal antiinflammatory agents are both effective for pain control in acute colic. Therapy with drugs that block (alpha)1-adrenergic receptors or calcium-channel blockers may facilitate passage of ureteral stones. In general, stones larger than 10 mm in diameter will not pass, and those smaller than 5 mm will.

Q: What recommendations can be made to reduce the risk of recurrent stone formation?

A: Patients should be advised to increase fluid intake to at least 2 liters daily and reduce sodium intake to 2300 mg or less and protein intake to 0.8 to 1 g per kilogram of body weight per day, since these dietary interventions have reduced stone recurrence in randomized trials. Calcium intake should not be reduced below the recommended intake for sex and age. Thiazide-type diuretics decrease urine calcium excretion, and in randomized, controlled trials, these medications significantly reduced recurrence rates of calcium stones by more than 50% during a 3-year period, as compared with placebo.

Table 4. Treatment Recommendations for the Prevention of Idiopathic Calcium Kidney Stones in Adults.

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