Calcium-Creatinine Ratio (Ca/Cr) in Pediatric Age
Calcium-Creatinine Ratio (Ca/Cr)
Key Points
- Non-invasive assessment of calcium excretion
- Useful screening tool for hypercalciuria
- Age-dependent reference ranges
- Sample from random or first morning urine
- Important in stone disease evaluation
Clinical Relevance
- Primary Indications:
- Nephrolithiasis evaluation
- Hypercalciuria screening
- Metabolic bone disease monitoring
- Vitamin D toxicity assessment
- Advantages:
- Avoids 24-hour collection
- Better compliance in children
- Cost-effective screening
- Rapid results
Physiological Basis
Calcium Homeostasis
- Regulatory Factors:
- Parathyroid hormone (PTH)
- Vitamin D
- Calcitonin
- Dietary intake
- Renal Handling:
- Glomerular filtration
- Tubular reabsorption
- Regulated excretion
Creatinine Production
- Determinants:
- Muscle mass
- Age
- Gender
- Physical activity
- Excretion Pattern:
- Relatively constant
- Minimal tubular handling
- Age-related variations
Measurement and Calculation
Sample Collection
- Timing Options:
- First morning void (preferred)
- Second morning void
- Random sample
- Collection Requirements:
- Clean catch specimen
- Proper storage
- Prompt analysis
Calculation Method
- Formula:
- Ca/Cr = (Urine Calcium mg/dL) / (Urine Creatinine mg/dL)
- Alternative units: mmol/mmol
- Unit Conversion:
- mg/mg × 2.27 = mmol/mmol
- mg/dL to mmol/L (calcium × 0.25)
- mg/dL to mmol/L (creatinine × 0.088)
Reference Ranges
- Age-specific Values:
- 0-6 months: <0.86 mg/mg
- 7-12 months: <0.60 mg/mg
- 1-3 years: <0.53 mg/mg
- 3-5 years: <0.39 mg/mg
- 5-7 years: <0.28 mg/mg
- >7 years: <0.21 mg/mg
Clinical Interpretation
Normal Values
- General Cutoffs:
- Adults: <0.14 mg/mg
- Children: Age-dependent
- Neonates: Higher ratios normal
- Influencing Factors:
- Dietary calcium intake
- Time of day
- Physical activity
- Season (vitamin D)
Elevated Ratios
- Primary Causes:
- Idiopathic hypercalciuria
- Vitamin D excess
- Primary hyperparathyroidism
- Renal tubular disorders
- Secondary Causes:
- Loop diuretics
- Glucocorticoids
- Immobilization
- Ketogenic diet
Clinical Applications
Screening Applications
- Primary Screening:
- Recurrent UTIs
- Abdominal pain
- Hematuria workup
- Family history of stones
- Monitoring:
- Response to therapy
- Dietary modifications
- Medication effects
Specific Conditions
- Nephrolithiasis:
- Initial evaluation
- Risk assessment
- Prevention monitoring
- Bone Disorders:
- Osteoporosis assessment
- Vitamin D management
- Metabolic bone disease
Limitations and Pitfalls
Technical Limitations
- Sample Issues:
- Storage conditions
- Temperature effects
- Processing delays
- Analytical Factors:
- Method variations
- Inter-laboratory differences
- Quality control importance
Clinical Limitations
- Confounding Factors:
- Dietary variations
- Exercise effects
- Medication influences
- Hydration status
- Interpretation Challenges:
- Age-specific variations
- Circadian rhythm effects
- Individual variability
- Disease states impact
Best Practice Recommendations
- Standardized Collection:
- Consistent timing
- Proper patient preparation
- Standard handling procedures
- Result Interpretation:
- Use age-specific ranges
- Consider clinical context
- Serial measurements when needed
- Correlate with other findings
