Related Self Assessment Questions A 36-year-old man presents to the emergency room with renal colic. A radiograph reveals a 1.5-cm stone. Which of the following statements regarding this disorder is correct? A. Conservative treatment including hydration and analgesics will not result in a satisfactory outcome. B. Serial kidney-ureter-bladder (KUB) radiographs should be used to follow this patient. C. Urinalysis will nearly always reveal microhematuria. D. When the acute event is correctly treated, this disease seldom recurs. E. Elevated blood urea nitrogen (BUN) and creatinine are expected. EXPLANATION: Initial management of kidney stones should include hydration and analgesics. However, as this patient's stone is larger than 1 cm, it is unlikely to pass spontaneously, though stones smaller than 0.5 cm usually do pass spontaneously. The size of the stone also makes a high-grade obstruction more likely; therefore, an intravenous pyelogram (IVP) must be urgently performed. A high-grade obstruction will require nephrostomy or a ureteral stent. If the stone is completely occluding the lumen of the ureter, urinalysis may not show microhematuria and thus may be misleading. Approximately 50% of patients may have a recurrence within 5 to 10 years. If both kidneys are functioning, then obstruction of one ureter will not result in an elevation in BUN and creatinine; such findings are expected only in the setting of an obstructed single functioning kidney. The answer is A. A 50-year-old man has recurrent stones that cannot be seen on plain film of the abdomen but are readily apparent on CT scan (renal stone protocol). The urinalysis is clear but the urine pH is 4.88 on a 24-hour urine specimen. What is the most likely type of stone that occurs in this clinical situation? A. Calcium phosphate B. Calcium oxalate C. Cystine D. Struvite E. Uric acid F. Xanthine G. Bilirubin EXPLANATION: Uric acid stones are associated with low urine pH, owing to decreased NH3 production by the kidney. Uric acid is underexcreted in an acid urine. These stones are commonly radiolucent on plain film or IVP but are easily visualized on CT. They often dissolve within weeks if the urine is alkalinized (eg, with potassium citrate). Struvite stones are found if the urine is infected with organisms (especially Proteus species) that produce the enzyme urease. Urease splits urea to CO2 and ammonium; the latter produces the characteristic alkaline urine (urine pH usually 8). The ammonium combines with urinary magnesium and phosphate to form the insoluble struvite (magnesium ammonium phosphate).These stones are opaque and are often large, filling the collecting system (staghorn calculi). Calcium containing stones cause over 70% of kidney stones and are radiopaque. Hypercalciuria and hyperoxaluria (as can be seen in intestinal malabsorption) are contributing factors. Hexagonal urinary crystals are found in cystinuria, an uncommon hereditary disease that starts early in life and if untreated progresses to end-stage renal disease. These stones may be lucent or opaque. Xanthine stones are rare. The pigment calcium bilirubinate causes gallstones, not kidney stones. The answer is E.
