Calculi - urinary

Last updated: Thursday, 08, April, 2004

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Item Process
Specimen

Calculus obtained from spontaneous passage or surgical intervention

Method

Commonly a series of spot tests are performed on pulverised, dissolved calculus. The mineral composition is then deduced from the relative amounts of each compound.

Calcium:spectrophotometry, atomic absorption spectrophotometry
Phosphate: spectrophotometry
Urate: spectrophotometry
Oxalate: spectrophotometry, titration
Ammonium: spectrophotometry
Cystine: visual, qualitative test
Xanthine: spectrophotometry
Carbonate: visual, qualitative test

Infrared spectroscopy and X-ray diffraction provide more definitive identification.

Application

Identification of risk factors for stone recurrence. May guide extracorporeal lithotripsy.

Interpretation

Stones containing calcium may indicate hypercalciuria.

Uric acid stones, or stones with a uric acid nidus, may indicate strongly acidic overnight urine or hyperuricosuria.

Oxalate stones may indicate hyperoxaluria. Magnesium ammonium phosphate ('triple phosphate') stones indicate bacterial infection.

Cystine stones indicate cystinuria.

Xanthine stones indicate xanthinuria or treatment with allopurinol.

Stones that do not dissolve in acid are usually factitious.

Reference

Coe FL et al.N Engl J Med 1992; 327: 1141-1152.

Tiselius HG et al. Eur Urol 2001; 40(4): 362-3671.