A 22-year-old man comes to the physician for a follow-up after the passage of a kidney stone. He was evaluated in the emergency department 10 days ago for right-sided colicky flank pain. An abdominal CT scan at that time revealed a 7-mm stone at the right ureteropelvic junction and two stones near the tips of calyces in the left kidney. The patient spontaneously passed the stone, but was not able to retrieve it for analysis. He has not previously had symptoms of kidney stones. His review of systems is normal. He is in good health, takes no medication or vitamins, is not chronically dehydrated, and has no family history of kidney stones.
Physical examination shows no abnormalities. Urinalysis shows occasional hexagonal crystals with benzene ring morphology.
Which of the following analyses performed on a 24-hour urine collection is most likely to lead to the diagnosis?

Question

A 22-year-old man comes to the physician for a follow-up after the passage of a kidney stone.  He was evaluated in the emergency department 10 days ago for right-sided colicky flank pain.  An abdominal CT scan at that time revealed a 7-mm stone at the right ureteropelvic junction and two stones near the tips of calyces in the left kidney.  The patient spontaneously passed the stone, but was not able to retrieve it for analysis.  He has not previously had symptoms of kidney stones.  His review of systems is normal.  He is in good health, takes no medication or vitamins, is not chronically dehydrated, and has no family history of kidney stones.
Physical examination shows no abnormalities.  Urinalysis shows occasional hexagonal crystals with benzene ring morphology.
Which of the following analyses performed on a 24-hour urine collection is most likely to lead to the diagnosis?

Quizplus · Accepted Answer

11ec193a_98f0_fb73_853d_9f5495204233_MD0002_00 The table above summarizes the clinical presentation of the common types of kidney stones. In a young patient with several kidney stones and typical cystine (hexagonal green/yellow) crystals on urinalysis, cystinuria is the most likely diagnosis. Cystinuria is a rare autosomal recessive disease that can lead to multiple kidney stones and complications such as obstructive uropathy, urinary tract infections, and loss of kidney function. Increased fluid intake to produce a higher urine volume, alkalinization of the urine (with potassium citrate or bicarbonate), and chelating agents (in some cases) can prevent further cystine stone formation. Patients with large stones or with urinary obstruction require referral to urology for stone removal. (Choice A) In the United States, >80% of the stones passed contain calcium. Hypercalciuria is a common predisposing factor in calcium-containing stone formers. Examination shows envelope-shaped crystals. (Choice B) Citrate appears to slow the growth of calcium crystals, and low urinary excretion of citrate is a factor that can contribute to stone formation. Urinary citrate measurement is not diagnostically helpful in this patient with cystinuria. (Choice D) Increased urinary excretion of oxalate is seen in inherited oxalate metabolism disorders and in malabsorption. In this patient with cystine crystals on urinalysis, measurement of the urinary excretion of oxalate is not diagnostically helpful. (Choice E) Increased urinary excretion of uric acid, along with low pH, contributes to uric acid stone formation. In some cases, increased urinary excretion of uric acid may also contribute to calcium stone formation by decreasing the solubility of calcium oxalate. Examination shows rhomboid crystals. Educational objective: Suspect cystinuria in patients with large branched calculi or a first stone occurring at an early age (childhood or adolescence). Hexagonal (benzene ring) crystals are seen in 25% of the patients on initial urinalysis. Increased fluid intake, alkalinization of the urine (with potassium citrate or bicarbonate), and chelating agents (in some cases) can prevent further cystine stone formation. __________ References: Reduced renal function and benefit of treatment in cystinuria vs other forms of nephrolithiasis (http://www.ncbi.nlm.nih.gov/pubmed/16686727) Cystinuria (http://www.ncbi.nlm.nih.gov/pubmed/18359399)

A 22-Year-Old Man Comes to the Physician for a Follow-Up