Alkaline Phosphatase (ALP) Test
Alkaline Phosphatase (ALP) Test in Pediatrics
Key Points
- ALP levels vary significantly with age and growth velocity in children
- Peak levels occur during infancy and puberty
- Bone and liver isoenzymes predominate in pediatric populations
- Critical for bone metabolism assessment and liver function monitoring
Normal Ranges by Age
- Newborns: 150-400 U/L
- Infants (1-12 months): 150-450 U/L
- Children (1-9 years): 125-320 U/L
- Adolescents:
- During growth spurt: 300-850 U/L
- Post-growth spurt: 100-300 U/L
Biochemistry and Function
- Major Isoenzymes:
- Bone-specific ALP (BALP): 80-90% in growing children
- Liver ALP: 10-20% in children
- Intestinal ALP: minimal contribution
- Placental ALP: relevant only in newborns
- Physiological Roles:
- Hydroxyapatite crystal formation
- Calcium and phosphate homeostasis
- Bone mineralization
- Collagen synthesis regulation
Growth-Related Changes
ALP variations correlate with:
- Growth velocity
- Pubertal stage
- Bone turnover rate
- Skeletal maturation
Clinical Indications
Elevated ALP Assessment
- Bone Disorders:
- Rickets
- Healing fractures
- Osteogenesis imperfecta
- Bone malignancies
- Liver Conditions:
- Biliary obstruction
- Hepatitis
- Drug-induced liver injury
Decreased ALP Investigation
- Genetic Conditions:
- Hypophosphatasia
- Wilson's disease
- Nutritional Deficiencies:
- Zinc deficiency
- Severe malnutrition
Result Analysis
Elevated ALP Interpretation
- Physiological causes:
- Growth spurts
- Bone healing
- Early pregnancy
- Pathological elevations:
- 2-3x normal: Suggest investigation
- 3-5x normal: Significant pathology likely
- >5x normal: Urgent evaluation needed
Additional Testing Considerations
- Concurrent tests:
- Calcium and phosphorus
- Vitamin D levels
- Liver function tests
- PTH levels when indicated
Special Considerations
Pre-analytical Variables
- Timing considerations:
- Diurnal variation
- Growth phase assessment
- Recent physical activity
- Sample handling:
- Temperature sensitivity
- Storage conditions
- Processing time
Monitoring Considerations
- Serial measurements:
- Timing intervals
- Growth rate correlation
- Treatment response assessment
- Documentation needs:
- Growth velocity
- Pubertal stage
- Recent illnesses
- Medication changes
