Normal Alkaline Phosphatase (ALP) Levels
The normal ALP level in adults is approximately 40-120 U/L, though this varies significantly by age, sex, and race/ethnicity.
Age- and Sex-Specific Reference Ranges
Adults (>18 years)
The most recent and comprehensive data from 2026 established a uniform reference interval of 40-120 U/L across multiple laboratory methods, which has been implemented clinically 1.
Race/Ethnicity Variations (Important Clinical Consideration)
Upper limits of normal vary substantially by race/ethnicity 4:
- Hispanic: 123.2 U/L (females), 123.8 U/L (males)
- African American: 109.9 U/L (females), 116.3 U/L (males)
- White: 97.1 U/L (females), 109.6 U/L (males)
- Asian American/Pacific Islander: 93.8 U/L (females), 95.3 U/L (males)
This represents a critical pitfall—using a single reference range may lead to misclassification of elevated ALP in Hispanic and African American patients.
Pediatric Populations
ALP levels are physiologically elevated in children due to bone growth 5, 2:
- Neonates (<15 days): 110-295 U/L 2
- Infants (15 days-1 year): 80-400 U/L 2
- Children (1-10 years): 90-290 U/L 2
- Adolescents (10-15 years): 75-300 U/L 2
Special Populations
Pregnancy: Levels up to twice the upper limit of normal (up to 232 U/L) can be physiologically normal due to placental production 3.
Clinical Context for Interpretation
When evaluating elevated ALP, the ACR guidelines emphasize determining hepatic versus non-hepatic origin 5:
- Hepatic origin confirmed by: Concomitantly elevated gamma-glutamyl transpeptidase (GGT), which is not present in bone 5
- Non-hepatic sources: Bone (Paget's disease, metastases, fractures), intestine, kidneys, placenta 5, 6
Common pitfall: Isolated intestinal ALP elevation can occur as a benign finding in asymptomatic individuals, mimicking hepatobiliary disease 6. Always consider isoenzyme analysis when ALP is elevated without clear hepatic or bone pathology.
The severity classification for hepatic ALP elevation follows the pattern used for aminotransferases: mild (<5× upper limit), moderate (5-10× upper limit), and severe (>10× upper limit) 5.