Calcium/Creatinine Ratio, Urine

Diagnostic Use

Calcium is an electrolyte which plays an important role in many physiological processes throughout the body. In normal health, almost all of the filtered calcium is reabsorbed in the post-glomerular nephron.

Urinary calcium excretion exhibits diurnal variation, largely reflecting dietary intake. As such, a 24 hour collection is the best way to assess urine calcium status. If testing is to be carried out on a random urine specimen, the measured calcium should be corrected for urine concentration and reported as the calcium/creatinine ratio.

Department

Core Biochemistry

Delphic Registration Code

UCAC

Constituent Tests

• Calcium, Urine
• Creatinine, Urine

Turnaround Time

3 hours

Test Code

4205

Specimen Type

• Urine

Specimen Requirements

Tube/Container Type:

Preferred

• Pottle

Acceptable

• 24hr Urine Container

Paediatric Specimen Requirements

Tube/Container Type:

Preferred

• Pottle

Acceptable

• 24hr Urine Container

Preferred Sample Volume (ml)

0.5

Additional Specimen Information

A fasting specimen is preferred.

Random urine collections are not required to be acidified on receipt to laboratory.

Aliquot Instructions

Sample Type

• Urine

Transport to Lab

Ambient (8 - 24 degrees Celsius)

Interpretation

Hypercalciuria increases the risk of developing kidney stones.  Urine calcium measurement is included as part of a “stone screen” in patients with unexplained nephrolithiasis or nephrocalcinosis.  Because of the large intra-individual variation in urinary calcium excretion, it is recommended to measure urine calcium on several separate occasions.

As mentioned above, 24 hour urine calcium is generally considered to be more accurate than the urine calcium/creatinine ratio.  Patients with an elevated/borderline ratio may benefit from follow up with a timed collection to confirm the urine calcium status.

Causes of hypercalciuria include hyperparathyroidism, type 1 renal tubular acidosis, Paget’s disease, malignancy, prolonged immobilisation and autosomal dominant hypocalcaemia.

Causes of hypocalciuria include familial hypocalciuric hypercalcaemia and thiazide diuretics.

Reference Intervals

Normal urinary Ca/Cr: 0.06 – 0.45

Test Method

Both tests are spectrophotometric assays performed on the Beckman Coulter AU5822 chemistry platform.

Contact Canterbury Health Laboratories on +64 3 364 0484 or email LabInfo@cdhb.health.nz

Contact Information

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