ALP (alkaline phosphatase) test: normal range

ALP is an enzyme, a protein that speeds up chemical reactions. It is found in every tissue, with the highest amounts in the liver, bile ducts and bone, and each part of the body makes a slightly different form. The blood test measures the total, so on its own it cannot say which tissue the ALP came from.

When the source matters, a doctor can order an ALP isoenzyme test, which separates liver, bone, intestinal and placental ALP, or a GGT test, which rises with liver ALP but stays normal when bone is the source.

Doctors use ALP to screen for or help diagnose liver and bone disease. It is part of the comprehensive metabolic panel and most liver function tests, so it is often flagged on routine bloodwork; it is also ordered for symptoms such as jaundice, upper right belly pain, itching, unexplained bone pain or fractures.

A high ALP is usually followed by other tests, such as GGT, bilirubin and the liver enzymes, and sometimes imaging, before any conclusion is drawn.

ALP changes with age, pregnancy, meals and medicines, not only with disease.

• Children and teenagers have naturally higher ALP because their bones are growing; during growth spurts it can reach about 500 IU/L, so adult ranges do not apply to them.
• ALP rises in the second and third trimesters of pregnancy because the placenta makes its own form; this is expected, not a sign of disease.
• A fatty meal before the test can raise ALP a little, particularly in people with blood group O or B, so fasting is often requested.
• Statins, some anti-seizure medicines and some antibiotics can raise ALP, and some other medicines lower it. Do not stop a medicine unless your doctor tells you to.
• Low zinc or magnesium can lower ALP, because the enzyme depends on zinc.
• Healing fractures, bone disorders, blocked bile ducts and liver disease are the groups of causes doctors consider for a high value.