Expansion
Liver, bone, placenta or gut, distinguished by GGT and clinical context
Expansion
Hepatobiliary (GGT also raised)
- Biliary obstruction: stones, tumour, stricture
- Primary biliary cholangitis, primary sclerosing cholangitis
- Drugs, infiltration, metastases
Bone (GGT normal)
- Paget disease: characteristically a very high ALP with normal calcium and phosphate
- Osteomalacia and rickets
- Bone metastases, healing fracture, hyperparathyroidism
- Normal growth in children and adolescents, where levels several times the adult range are expected
Physiological
- Pregnancy, third trimester, from placental production
Other: ALP can be low in hypophosphatasia, malnutrition, hypothyroidism, Wilson disease and zinc deficiency.
If the source remains unclear, isoenzyme analysis separates the fractions directly.
A useful discipline is to interpret ALP alongside GGT, calcium, phosphate and the clinical picture rather than in isolation, since it is one of the most commonly abnormal results on routine testing and the great majority have a benign explanation.