Biomarker · Liver

ALP (alkaline phosphatase)

Also known as: ALP, alkaline phosphatase, alk phos

An enzyme made mainly by the cells lining the bile ducts and by bone-forming cells. A raised level with a raised GGT points to obstructed bile flow (cholestasis); a raised level with a normal GGT points to bone, growth or pregnancy.

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Also known as: ALP, alkaline phosphatase, alk phos
Units: U/L (units per litre); much higher in growing children
Measured by: Liver function tests

What it is and what it does

Alkaline phosphatase is anchored to the membranes of bile-duct cells, osteoblasts in bone, the placenta and the gut lining. When bile flow is obstructed, by a gallstone in the common bile duct, a tumour of the pancreas head or bile ducts, or by drugs that impair bile secretion, the liver makes far more ALP and releases it into blood. Growing children and adolescents have naturally high bone ALP, as do people healing a fracture, and the placenta raises it in the third trimester of pregnancy. Distinguishing liver from bone ALP relies on the GGT (raised only in the liver pattern) or on measuring the separate isoenzymes.

Why it may be higher

Cholestasis: bile-duct stones, strictures, pancreatic or biliary cancer, primary biliary cholangitis, primary sclerosing cholangitis
Liver infiltration or abscess, cirrhosis, some drugs (for example flucloxacillin, co-amoxiclav)
Bone: Paget disease, fracture healing, osteomalacia, bone metastases, hyperparathyroidism
Growth in childhood and adolescence, third-trimester pregnancy

Why it may be lower

Hypophosphatasia (rare inherited deficiency)
Hypothyroidism, zinc or magnesium deficiency, malnutrition, some anaemias

A high or low value can be associated with several different situations. The result is interpreted with other results, symptoms, history and clinical findings.

What can affect the result

Age (children and adolescents), pregnancy, blood group and a recent fatty meal in some people
Fracture healing and bone growth
Sample handling

Reference ranges. Reference intervals for this marker depend on the laboratory, the assay, the units, age, sex and pregnancy. Interpret a result against the interval printed on the laboratory report, not against a figure from the internet.

Medicines that can change it

Amoxicillin

Each medicine page lists its effect on this marker under "Effects on tests and results", with the source.

Educational content. A biomarker page explains what a substance is and why its level can change. It cannot determine the cause of your result: interpret a result using the range supplied by the laboratory that performed the test, with the clinician who ordered it.