ALP (Alkaline Phosphatase)
Complete guide to ALP testing — normal ranges, causes of high alkaline phosphatase, and when to get tested.
What is ALP?
Alkaline phosphatase (ALP) is an enzyme found in the liver, bones, kidneys, and digestive system. Elevated ALP can indicate liver disease, bone disorders, or bile duct obstruction.
Why is it Important?
ALP is used to:
- Detect liver or bile duct problems
- Diagnose bone disorders (Paget's disease, osteomalacia)
- Monitor bone growth in children and adolescents
- Assess effectiveness of treatment for bone or liver disease
Normal Ranges
| Group | Range | Unit |
|---|---|---|
| Adult | 30 – 120 | U/L |
| Adolescent (growing bones) | 100 – 400 | U/L |
| Pregnancy (3rd trimester) | Up to 2× normal | U/L |
What Do Abnormal Results Mean?
High ALP
Common causes include:
- Liver/Bile Duct: Bile duct obstruction, cholestasis, cirrhosis, hepatitis
- Bone: Paget's disease, bone cancer, osteomalacia, healing fractures
- Other: Hyperparathyroidism, hyperthyroidism, pregnancy
- Medications: Antibiotics, anti-seizure drugs
Differentiating Liver vs Bone ALP
If ALP is elevated, additional tests help identify the source:
- GGT elevated: Liver origin
- GGT normal: Bone origin
- Bone-specific ALP test: Direct measurement
Low ALP
Less common, but can indicate:
- Malnutrition or vitamin deficiencies
- Hypophosphatasia (rare genetic disorder)
- Hypothyroidism
- Magnesium or zinc deficiency
When Should You Get Tested?
ALP is part of routine liver function tests and comprehensive metabolic panels. Your doctor may order it if you have symptoms like jaundice, abdominal pain, bone pain, or unexplained fractures.
This information is for educational purposes only and is not a substitute for professional medical advice.
Last reviewed: 2026-02-13