RENAL COLIC AND DIETARY RECOMMENDATIONS

Patients with renal colic account for nearly 1 million visits to emergency departments (EDs) in the United States annually.^[1-3] According to 1 study, the estimated lifetime risk of developing a kidney stone is approximately 12% for white men.^[2,3] Approximately 50% of patients with previous urinary calculi have a recurrence within 10 years.^[4]

Calcium oxalate stones are the most common stone encountered by practicing emergency physicians.^[5] Discharge instructions for patients who are stable for outpatient treatment often include discussion of hydration and pain control, along with medications to potentially facilitate passage of the stone.

The optimal diet for patients able to be safely discharged from the ED may not be commonly discussed with patients, but it has the potential to affect recurrence of renal calculi and return visits to the ED.

Because calcium oxalate is the most common component of kidney stones, an increase in urinary oxalate increases the risk for calcium oxalate concentration and subsequent stone formation to a greater degree than urinary calcium. Urinary oxalate is derived from 2 separate sources: endogenous synthesis and diet. The foods highest in oxalate content are spinach, rhubarb, beets, chocolate, nuts, concentrated brans, legumes, soy, tea, sesame seeds, parsley, and berries. Avoidance of these foods with promotion of adequate hydration may help to reduce recurrent stone formation.^[6]

Additional research also suggests that reducing dietary sodium intake may have a role in preventing incident kidney stones.^[7] High amounts of salt intake combined with inadequate hydration increase risk for stone formation.

Consumption of calcium-rich foods (ie, dairy products) in moderate amounts helps to bind oxalic acid, further reducing oxalate absorption, a known factor in calcium oxalate stone formation.^[7] This recommendation, however, does not apply to individuals who absorb excess dietary calcium from the intestine. In those cases, restricting calcium intake is useful.

Recommendations to consume generous amounts of water (2.5- 3 L daily) as a preventative measure have been advocated for patients in whom kidney stones form. Multiple studies recommend patients to maintain urine output > 1 L/day to reduce the recurrence of renal colic.^[8]

Interestingly, and contrary to popular belief, multiple observational studies have found that consumption of coffee, tea, beer, and wine in moderation are associated with a reduced risk for stone formation.^[9,10]

Although previous data and observational studies have suggested an increased risk for stone formation associated with soda consumption, after adjusting for other diet-related issues, soda consumption (caffeine-free soda, diet soda, and regular soda) was not associated with an increased risk for stone formation as described in 2 studies.^[9,10]

Additional studies have also demonstrated that consumption of orange juice as well as lemonade can increase urinary citrate concentrations and pH, thereby reducing risk for stone formation.^[11]

Based on a recent study, orange juice is preferred over lemonade and cranberry juice due to greater alkalinizing potential and ability to increase urinary citrate excretion, resulting in greater stone solubility.^[11]

An alternative intervention for patients who suffer from recurrent calcium stones is the addition of potassium citrate as a dietary supplement. Potassium citrate prevents recurrent calcium kidney stones by increasing urinary pH, which enhances urinary citrate excretion; high urinary citrate concentrations increase the solubility of stone-forming salts.^[12]

Conclusions

Dietary oxalate contributes up to 50% of urinary oxalate for typical diets. Dietary restriction of oxalates is effective in reducing urinary oxalate and consequently stone recurrence in most patients in whom kidney stones form.

Simultaneous consumption of calcium-rich foods in moderate amounts further reduces oxalate absorption from oxalate-containing foods.

Reduction in dietary salt intake and careful attention to adequate hydration to ensure urine output > 1 L/day are also critical to reduce recurrence of calcium stones.

The addition of 1 serving of daily citrus juice (orange juice preferred over lemonade), or the use of potassium citrate as a supplement, may also help to reduce stone recurrence in patients who have recurrent kidney stones.