Normal Values for Spot Calcium:Creatinine Ratio
The normal upper limit for spot urine calcium:creatinine ratio varies by age, with values declining from infancy through childhood: <1 year: 2.2 mmol/mol (1.5 mg/mg), 1-3 years: 1.4 mmol/mol (1.25 mg/mg), 3-5 years: 1.1 mmol/mol (1.0 mg/mg), 5-7 years: 0.8 mmol/mol (0.70 mg/mg), and >7 years: 0.7 mmol/mol (0.60 mg/mg). 1
Age-Specific Reference Ranges
Pediatric Population (Birth to 18 years)
The calcium:creatinine ratio is age-dependent and declines progressively during the first five years of life, except during the newborn period 2:
- <1 year: Upper limit 2.2 mmol/mol (1.50 mg/mg) 1, 3
- 1 to <2 years: Upper limit 1.4 mmol/mol (1.25 mg/mg) 1, 3
- 2 to <5 years: Upper limit 1.1 mmol/mol (1.00 mg/mg) 1, 3
- 5 to <7 years: Upper limit 0.8 mmol/mol (0.70 mg/mg) 1, 3
- >7 years to 18 years: Upper limit 0.7 mmol/mol (0.60 mg/mg) 1, 3
Adults
For adults, the normal calcium:creatinine ratio is generally <0.60 mmol/mol (0.53 mg/mg) 3. Some sources suggest hypercalciuria is present when the ratio exceeds 0.23 mg/mg in 24-hour collections 4.
Optimal Timing for Sample Collection
First morning spot urine samples are preferred for children and adolescents to avoid confounding effects of orthostatic proteinuria and provide the most reliable results 1. Research demonstrates that evening and first morning spot samples show the strongest correlation with 24-hour urinary calcium excretion (correlation coefficients of 0.64 and 0.71, respectively) 5.
For practical screening purposes:
- First morning void: Lowest coefficient of variation and best correlation with 24-hour excretion 5
- Second morning sample (3 hours after breakfast): Acceptable alternative with reliable diagnostic accuracy 4
- Avoid second morning samples immediately after waking: Lower correlation (0.52) compared to first morning 5
Important Clinical Considerations
Factors Affecting Accuracy
Several conditions can falsely elevate the calcium:creatinine ratio 1:
- Dehydration (concentrated urine with creatinine >40 mg/dL may show falsely normal ratios) 6
- Vigorous exercise within 24 hours
- Fever or acute illness
- Marked hyperglycemia
- Symptomatic hypercalcemia (especially in first 2 years of life)
Confirmation Requirements
A single elevated value should not be used to diagnose hypercalciuria. Repeat testing is essential because of high biological variability in urinary calcium excretion 2, 4. The diagnosis requires confirmation with at least 2 of 3 samples collected over time 4.
Unit Conversion
When interpreting results, note that: