Nephrolithiasis

Nephrolithiasis is a common cause of morbidity in the United States. The peak incidence is in the age group of 20 to 45 years, with a predilection for men(the incidence is five times higher in men than in women).

The incidence of nephrolithiasis is highet in developed countries, mainly because of high intake of animal protein coupled with a low-fiber diet. Depending on stone composition, five types of renal calculi are recognized. Calcium stones are the most common, accounting for 75% of all stone. The majority of these are calcium oxalate stones, which contribute to more than 50% of all diagnosed renal calculi.

Calcium phosphate stones require an alkaline pH for their precipitation and therefore are less common except in patients with RTA, primary hyperparathyroidism, or milk alkali syndrome. Patients with nephrolithiasis usually have hematuria(both gross and microscopic) and sudden onset of excruciating colicky pain located in the flank and radiating to the groin on the same side. Nephrolithiasis may sometimes be associated with polyuria, dysuria, vomiting, and ileus. Initial evaluation of the patient with nephrolithiasis should include past history of hematuria or passing a stone, urinary infections, family history, and a detailed dietary analysis. Initial screening should include measurements of electrolytes, creatinine, serum calcium phosphate, and uric acid. Management of patients with nephrolithiasis requires identification of the specific type of stone. Urinalysis is helpful in determining the PH, identifying hematuria ruling out infection, and, most important, identifying the type of crystals. An IVP with tomographic cuts can identify many of the stone types. Uric acid stones are easily identifiable because they are the only radiolucent stones. Cystine stones are less radiopaque and may assume the calyceal shape. Also, triple phosphate stones have a staghorn appearance and can be easily identified radiologically. The most reliable method of identifying stones is crystallographic study when the stone is identified through straining of urine. Forty percent of patients with a first episode of nephrolithiasis have a second episode within 2 to 3 years, and 75% have a recurrence in 7 to 10 years.

After 20 years of follow-up, less than 10% of the patients remain stone free. On the basis of these figures, all patients with a first episode of nephrolithiasis should be advised to consume approximately 3 L of fluid per day to maintain at least 2 L of urinary volume per day Eight to 10 ounces should be consumed during the night, because this is the period of maximum urinary concentration. Restricting intake of animal protein an reducing daily salt intake are the two dietary modifications that have been shown to lower the risk of recurrent nephrolithiasis.

Accordingly, patients should be advised to restrict their intake of protein to 1 to 1.5 g/kg and to use salt in moderation.

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