Alkaline phosphatase

This is the harmonised UK adult range; it is much higher in children and teenagers because bone is growing, and it rises in the later months of pregnancy.

Alkaline phosphatase is an enzyme made mainly in the liver's bile ducts and in bone, with smaller amounts from the gut and, in pregnancy, the placenta. Because two organs make it, a raised level can come from either, and doctors use other tests such as GGT or bone ALP to tell them apart. The test measures the total enzyme activity in a blood sample.

It is part of both the liver panel and the bone profile. Doctors use it when looking into liver, bile duct or gallbladder problems, bone conditions such as Paget's disease or vitamin D deficiency, and as part of general health checks.

• Growth in childhood and adolescence, and the later months of pregnancy
• Blockage or irritation of the bile ducts, including gallstones and some medicines
• Bone conditions where bone is being rebuilt: Paget's disease, healing fractures, low vitamin D
• Fatty liver and alcohol
• Overactive parathyroid or thyroid glands
• Some blood groups after a fatty meal, by a small amount

• Low zinc or magnesium
• Underactive thyroid
• Some rare inherited conditions
• Bisphosphonate medicines used for bone
• Malnutrition

• It is normally well above the adult range in anyone still growing
• A fatty meal before the test raises it slightly in people of blood group O or B
• A healing fracture raises it for several weeks

Fasting is not essential but a morning sample avoids the small rise after a fatty meal. Read alongside GGT (liver) and calcium, phosphate and vitamin D (bone).

Written by a UK consultant physician. Typical UK adult reference ranges; your laboratory's own printed range takes precedence.