A 50-year-old man comes to the emergency department due to sudden onset of severe, colicky pain in the right flank. He was admitted twice previously for similar symptoms. On both occasions, the patient was managed conservatively and sent home. He has no other medical problems and no history of urinary infections. He usually eats precooked food from a local store and has a soda with each meal. The patient does not use tobacco, alcohol, or illicit drugs. His vital signs are stable. He is given intravenous fluids and pain medications. Laboratory results are as follows: CT scan of the abdomen without contrast reveals renal calculi. Urinalysis shows moderate levels of blood and calcium oxalate crystals. Which of the following is the best recommendation for the prevention of future stones in this patient?

Question

A 50-year-old man comes to the emergency department due to sudden onset of severe, colicky pain in the right flank.  He was admitted twice previously for similar symptoms.  On both occasions, the patient was managed conservatively and sent home.  He has no other medical problems and no history of urinary infections.  He usually eats precooked food from a local store and has a soda with each meal.  The patient does not use tobacco, alcohol, or illicit drugs.  His vital signs are stable.  He is given intravenous fluids and pain medications.  Laboratory results are as follows:  CT scan of the abdomen without contrast reveals renal calculi.  Urinalysis shows moderate levels of blood and calcium oxalate crystals.  Which of the following is the best recommendation for the prevention of future stones in this patient?

Quizplus · Accepted Answer

The most common renal stones are calcium stones. Increased sodium intake enhances calcium excretion (hypercalciuria), and low sodium intake promotes sodium and calcium reabsorption through its effect on the medullary concentration gradient. Reabsorption of sodium and calcium is coupled via complex mechanisms involving the calcium-sensing receptor in the thick ascending limb of the loop of Henle. Therefore, patients with recurrent renal calculi should be advised to restrict sodium intake. If these patients continue to develop renal stones, their urine sodium levels may be checked to evaluate adherence to a sodium-restricted diet. (Choices A and F) Excessive calcium intake (>2 g/day) and increased fructose intake may worsen hypercalciuria and calcium oxalate precipitation in urine. Hydrochlorothiazide reduces urinary calcium excretion and may be used in recurrent stone formers with hypercalciuria. (Choices B and E) Calcium binds oxalate to form inabsorbable calcium oxalate in the gastrointestinal tract. Calcium restriction may increase free oxalate absorption, leading to hyperoxaluria and urinary calcium oxalate stone formation. Increased vitamin C intake also promotes hyperoxaluria. Patients should be advised to restrict oxalate-containing foods (eg, chocolate, tea, peanuts). (Choice C) A high-potassium diet decreases urinary calcium excretion. Foods rich in potassium enhance urinary citrate excretion (likely from urinary alkalization), forming soluble calcium citrate and thereby preventing stone formation. (Choice D) Diets rich in animal protein are associated with an increased risk of nephrolithiasis in men. Increased acid resulting from protein metabolism is excreted in urine, leading to calcium salt precipitation. (Choice H) Patients with malabsorption syndromes (eg, Crohn disease, cystic fibrosis) have increased amounts of intestinal fatty acids that form salts with calcium. Less calcium is available to bind oxalate, resulting in hyperoxaluria. This patient has no evidence of malabsorption. Educational objective: The dietary recommendations for patients with renal calculi are: Increased fluid intakeDecreased sodium intakeNormal dietary calcium intake Increased fluid intake Decreased sodium intake Normal dietary calcium intake References: Diet and fluid prescription in stone disease. (http://www.ncbi.nlm.nih.gov/pubmed/16837923)

A 50-Year-Old Man Comes to the Emergency Department Due to Sudden