Specimen Collection: Random urine samples may be used. Simultaneously measure calcium and creatinine in the samples.
renal calcium clearance =
= (urine calcium in mg/dL) * (24 hour urine volume in mL) / ((serum calcium in mg/dL) * (minutes in 24 hours))
renal creatinine clearance =
= (urine creatinine in mg/dL) * (24 hour urine volume in mL) / ((serum creatine in mg/dL) * (minutes in 24 hours))
renal calcium to creatinine clearance ratio =
= (urine calcium in mg/dL) * (serum creatinine in mg/dL) / ((serum calcium in mg/dL) * (urine creatinine in mg/dL))
Significance: Patients with familial hypocalcuric hypercalcemia will have a clinical syndrome similar to hyperparathyroidism; however, they:
(1) do not respond to parathyroidectomy
(2) have a low renal calcium-creatinine clearance ratio (< 0.01)
This equation is the same as for the fractional excretion of calcium, which is reported in percent (derived by multiplying the ratio by 100%).
