Normal Range for 24-Hour Urinary Calcium Excretion
The normal upper limit for 24-hour urinary calcium excretion is approximately 200-300 mg/day in adults, though this varies by sex, race, and dietary intake, with values below 200 mg/day generally considered normal when dietary factors are controlled. 1
Adult Reference Ranges
General Population
- Standard laboratory reference range: 100-300 mg/24 hours is commonly used, though this may not reflect optimal age- and race-specific values 2
- Optimal cutoff on controlled diet: approximately 172-200 mg/day represents the upper limit when dietary calcium, sodium, and protein are standardized 1
- Mean excretion in healthy adults: 200-300 mg/dL with a calcium/creatinine ratio of 0.07-0.15 3
Sex and Race-Specific Ranges
The reference intervals differ significantly by demographic factors:
White women: 2
- Younger (25-45 years): 23-287 mg/24 hours
- Older (55-90 years): 37-275 mg/24 hours
Black women: 2
- Younger (25-45 years): 8-285 mg/24 hours
- Older (55-90 years): 7-225 mg/24 hours
Black women demonstrate consistently lower urinary calcium excretion compared to white women across all age groups. 2
Pediatric Reference Ranges
Weight-based measurement: 4 mg/kg/day represents the threshold for hypercalciuria in children, with 8.6% of healthy children exceeding this value and only 1.5% exceeding 6 mg/kg/day. 4
Calciuria values (mg/kg/day) remain relatively constant throughout childhood except for a transient decrease during puberty, occurring earlier in girls than boys. 4
Clinical Context and Interpretation
Defining Hypercalciuria
Hypercalciuria in stone formers is classically defined as >200 mg/day on a restricted diet, though the optimal cutoff may be as low as 172 mg/day when dietary variables are controlled. 1 This definition is validated by clear demarcation between stone formers with absorptive hypercalciuria (mean 259±55 mg/day) and normal individuals (mean 127±46 mg/day) on standardized diets. 1
Important Caveats
Dietary influences significantly affect interpretation: 2, 1
- Urinary calcium correlates with calcium intake (r=0.12, p=0.001)
- Correlates with serum 1,25(OH)₂D (r=0.23, p<0.001)
- Correlates with calcium absorption (r=0.18, p=0.003)
- Does NOT correlate with serum 25OHD
Diurnal variation exists: Calcium excretion increases significantly at night compared to daytime values, and measurements should be interpreted accordingly. 3
Collection adequacy is critical: Volume and creatinine excretion must be measured to confirm complete 24-hour collection, as incomplete collections invalidate results. 5, 6
Spot Urine Alternative
Calcium/creatinine ratio on spot urine samples (morning or evening) correlates well with 24-hour excretion (r=0.83 for morning, r=0.81 for evening) and can efficiently screen for hypercalciuria when 24-hour collection is impractical. 7