Urinalysis Case Study - Cystinuria

Urinalysis Case Study - Cystinuria

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What is Cystinuria?

Cystinuria is an inherited condition characterized by the buildup of cystine in the kidneys and bladder. This amino acid accumulation indicates a disorder in reabsorption of cystine in the renal tubules. As a result, excess cystine crystallizes and forms stones as the urine becomes more concentrated.

Cystine stones account for 1-2% of adult urolithiasis and may be associated with urinary tract infection or obstruction. Cystine crystals are found in acidic urine and care should be taken to not confuse them with uric acid crystals. Cystinuria can be confirmed with the cyanide nitroprusside test.

Morphology/Features:

  • Hexagonal plates that are mostly equilateral
  • Generally non-birefringent
  • pH < 5.5
  • Nitroprusside reaction positive


Resources:

Color Atlas of the Urinary Sediment, College of American Pathologists, Northfield, IL. Atlas of Urinary Sediment, Sysmex Corporation, Kobe, Japan.



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