Specimen Collection

1. 24 hr urine collected in a plain or thymol container is the recommended sample for adults.

2. A spot urine in a plain container (for calcium/creatinine ratio).
   Request calcium and creatinine.

Sample stability:

• 2 days at 15-25 ^o C

• 4 days at 2-8 ^o C

• 3 weeks at -20 ^o C

Reference Intervals

Adult: 2.5 - 7.5 mmol/day (on average diet of calcium)

Age	calcium / creatinine ratio (mmol/mmol) *
6 m - 1 y	0.09 - 2.2
1 - 2 y	0.07 - 1.5
2 - 3 y	0.06 - 1.4
3 - 5 y	0.05 - 1.1
5 - 7 y	0.04 - 0.7
7-17 y	0.04 - 0.7
Adult:	< 0.6
* Note: calcium creatinine ratio is calculated differently and has a different guidance. See text below in this entry for interpretation.

Conversion factors : mg/100 mL x 0.25 = mmol/L
mmol/L x 4 = mg/100 mL

Uncertainty of measurement : 5%

Turnaround Time: Within 3 hours
Assay Method

Principle : Colorimetric

Reagents: Roche CA2 kit

Analyser: Cobas c702

Diagnostic Use and Interpretation

Renal calculi: Urine calcium should be measured in patients with renal stones to determine whether hypercalciuria is present (see Renal Stones). A 24 h urine provides the best diagnostic information. Spot urine samples (calcium/creatinine ratio) are less definitive, but can also give a useful indication as to whether hyper- or hypocalciuria is present.

Other indications : Urine calcium is usually high in hypercalcaemic states, and low in hypocalcaemia. Rare exceptions to this include mutations of the calcium-sensing receptor causing familial hypocalciuric hypercalciemia (FHH).

Calcium/creatinine clearance ratio (UCCR, fractional excretion of calcium): the UCCR may be useful in distinguishing FHH from primary hyperparathyroidism. This it not the same as the urine calcium/creatinine ratio. It requires both plasma and urine concentrations of calcium and creatinine measured together. The calcium/creatinine ratio (which requires only calcium and creatinine on a urine sample) is not the appropriate test.

FHH is an uncommon condition, usually associated with mild hypercalcaemia with upper normal or sometimes slightly increased PTH levels. Patients typically have a family history of hypercalcaemia from a young age. Confirmation can be made by sequencing of the calcium sensing receptor.

UCCR = (urine Ca x plasma creatinine) / (plasma Ca x urine creatinine x 1000)

where plasma creatinine is in umol/L and all other quantities are in mmol/L. The corrected plasma calcium value should be used.

The UCCR is typically <0.01 in FHH and >0.01 in primary hyperparathyroidism. Reported sensitivity is 85% and specificity 88% (there is a modest overlap). Ideally the analysis should be performed on a 24hr urine sample and paired serum sample for calcium and creatinine. It has not formally been validated on spot urine sample collects but is often used in this way. It is important to consider other causes of hypercalcaemia with relative hypocalciuria, e.g. thiazides or lithium treatment.

References :

1. Matos et al. Urine phosphate/creatinine, calcium/creatinine and Mg/creatinine ratios in a healthy paediatric population. J Pediatr 131:252-257, 1997.

2. Jayasena CN, Mahmud M, Palazzo F et al. Utility of the urine calcium-to-creatinine ratio to diagnose primary hyperparathyroidism in asymptomatic hypercalcaemic patients with vitamin D deficiency. Ann Clin Biochem;48:126-129

3. Urine calcium and serum ionized calcium, total calcium and parathyroid hormone concentrations in the diagnosis of primary hyperparathyroidism and familial benign hypercalcaemia. Gunn, Wallace. Ann Clin. Biochem. 1992 Jan;29 (Pt 1):52-8

Contact Information

Emails to chemicalpathologist@adhb.govt.nz will receive priority attention from the on-call chemical pathologist.

If the query concerns a specific patient please include the NHI number in your email.

If email is not a suitable option, please contact the on-call chemical pathologist via Lablink (Auckland City Hospital ext. 22000 or 09-3078995).

Individual chemical pathologists may be contacted but will not be available at all times.

After-hours : contact Lablink (Auckland City Hospital ext. 22000 or 09-3078995) or hospital operator for on duty staff after hours.

Dr Samarina Musaad (Clinical Lead) : SamarinaM@adhb.govt.nz ext. 22402

Dr Cam Kyle: CampbellK@adhb.govt.nz ext 22052

Dr Weldon Chiu: WeldonC@adhb.govt.nz ext. 23427

Dr Campbell Heron: CHeron@adhb.govt.nz ext. 23427

Dr Sakunthala Jayasinghe: Sakunthala@adhb.govt.nz ext. 23427

Last updated at 15:26:00 06/01/2025