Urinary Electrolytes Test
Urinary Electrolytes in Pediatric Patients
Urinary electrolyte measurement is a fundamental tool in evaluating fluid-electrolyte disorders, renal function, and acid-base status in pediatric patients.
Key Points:
- Essential for fluid balance assessment
- Critical in evaluation of kidney function
- Helps differentiate various pathological states
- Age-specific reference ranges crucial
- Collection method affects interpretation
Collection Types:
- 24-Hour Collection:
- Gold standard for quantitative assessment
- Complete instructions for caregivers
- Temperature-controlled storage
- Preservative requirements
- Random Spot Sample:
- More practical in children
- First morning void preferred
- Standardization with creatinine
- Multiple samples may be needed
- Timed Collections:
- 4-hour collections
- 8-hour collections
- 12-hour collections
- Indication-specific timing
Collection Guidelines:
- Patient Preparation:
- Age-appropriate instructions
- Dietary considerations
- Medication documentation
- Hydration status recording
- Quality Assurance:
- Volume measurement
- Time documentation
- Storage conditions
- Transport requirements
Essential Measurements:
- Sodium (Na+):
- Normal range: 40-220 mEq/L
- Age-specific variations
- Dietary influence significant
- Potassium (K+):
- Normal range: 25-125 mEq/L
- Diurnal variation present
- Diet-dependent changes
- Chloride (Cl-):
- Normal range: 110-250 mEq/L
- Correlates with sodium
- Important for acid-base assessment
Calculated Parameters:
- Fractional Excretion:
- FENa calculation
- FEK calculation
- Age-specific interpretations
- Transtubular Potassium Gradient:
- Formula: (U/P)K ÷ (U/P)osm
- Normal range: 8-9
- Clinical significance
Primary Indications:
- Fluid-Electrolyte Disorders:
- Dehydration assessment
- Hyponatremia evaluation
- Hyperkalemia investigation
- Salt-losing states
- Renal Disorders:
- Acute kidney injury
- Tubular disorders
- Nephrotic syndrome
- Renal tubular acidosis
- Endocrine Disorders:
- Adrenal insufficiency
- CAH evaluation
- Diabetes insipidus
Monitoring Applications:
- Therapeutic Response:
- Diuretic therapy
- Steroid treatment
- Fluid management
- Dietary Compliance:
- Salt restriction
- Potassium supplementation
- Protein intake
Pattern Recognition:
- Volume Depletion:
- UNa < 20 mEq/L (prerenal)
- UNa > 40 mEq/L (renal)
- FENa interpretation
- Potassium Disorders:
- High TTKG in hyperkalemia
- Low TTKG in hypokalemia
- Response to loading
- Acid-Base Disorders:
- Urinary anion gap
- Chloride response
- pH correlation
Common Patterns:
- Prerenal Azotemia:
- Low UNa, UCl
- High UK
- Low FENa
- ATN:
- High UNa, UCl
- Variable UK
- High FENa
- Salt-Losing Nephropathy:
- High UNa, UCl
- Variable UK
- Inappropriate FENa
Neonatal Considerations:
- Physiologic Changes:
- Higher fractional excretion
- Immature tubular function
- Different reference ranges
- Collection Challenges:
- Bag specimen issues
- Catheterization indications
- Volume requirements
Critical Situations:
- Emergency Assessment:
- Spot sample utility
- Rapid turnaround times
- Decision points
- Complex Cases:
- Multiple pathologies
- Medication effects
- Mixed disorders
