Urinary excretion of calcium shows a wide range of values, and is affected by dietary calcium and protein as well as urinary phosphate excretion.
Specimen Collection:
(1) urine specimens should be collected into 6 mol/L HCl (1-2 mL for random specimens; 20-30 mL for 24 hour specimens) to prevent precipitation of calcium salts
(2) urine specimens should be kept well mixed during collection
urinary calcium to creatinine ratio =
= (urinary calcium in mg/dL) / (urine creatinine in mg/dL)
urinary calcium as mg per dL of glomerular filtrate =
= (urinary calcium in mg/dL) * (serum creatinine in mg/dL) / (urine creatinine in mg/dL)
Interpretation:
• The normal urinary to creatinine ratio in healthy patients with constant muscle mass: <=0.14; vales > 0.20 can be seen in hypercalcuria.
• The normal urinary calcium as mg/dL glomerular filtrate: < 0.16 for spot fasting or timed specimens collected after an overnight fast.
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