Approach to the Patient with Nephrolithiasis;The Stone Quiz

Calcium oxalate stones are the most common type of stones in patients with idiopathicnephrolithiasis. A calcium phosphate stones are more typical of patients with renal tubular acidosis,chronic urinary tract infection and primary hyperparathyroidism.A non-contrast enhanced helical computed tomography (CT) scan of the abdomen is thediagnostic procedure of choice with superior sensitivity and specificity of almost 100% compared tothe KUB and abdominal ultrasound. Patients should be instructed to strain their urine and bring inany stone that passes for analysis. Stone identification enables better planning of subsequent therapy.The likelihood of stone passage is 95% for stones up to 5 mm in size. Stones larger than 5 mm indiameter that do not pass in several days merit referral to an urologist for lithotripsy, or lithotomy. Nospecific work-up or drug therapy is typically provided for patients who have passed a single stone.Long term management of patients who have passed their first stone includes recommendations toavoid a diet high in salt or animal protein and maintenance of a fluid intake greater than 2 liters perday. A low calcium diet is also an important risk factor for calcium nephrolithiasis. A low dietarycalcium intake reduces the concentration of calcium in the intestinal lumen which can lead to increasein gastrointestinal absorption and urinary excretion of oxalate. Patient with recurrent disease shouldreceive a complete evaluation to treat the identified risk factors and prevent stone formation.