When a person has evidence of liver disease, very high ALP levels can tell the doctor that the person’s bile ducts are somehow blocked. Often, ALP is high in persons who have cancer that has spread to the liver or the bones, and doctors can do further testing to see if this has happened. If a person with bone or liver cancer responds to treatment, ALP levels will decrease. When a person has high levels of ALP, and the doctor is not sure why, s/he may also order ALP isoenzyme tests to try to determine the cause.

ALP is generally part of a routine lab testing profile, often with a group of other tests called a liver panel. It is also usually ordered along with several other tests if a patient seems to have symptoms of a liver or bone disorder.

High ALP usually means that the bone or liver has been damaged. If other liver tests such as bilirubin, aspartate aminotransferase (AST), or alanine aminotransferase (ALT) are also high, usually the ALP is coming from the liver. If calcium and phosphate measurements are abnormal, usually the ALP is coming from bone.

In some forms of liver disease, such as hepatitis, ALP is usually much less elevated than AST and ALT. When the bile ducts are blocked (usually by gallstones, scars from previous gallstones or surgery, or by cancers), ALP and bilirubin may be increased much more than AST or ALT. In a few liver diseases, ALP may be the only test that is high.

In some bone diseases, such as a disorder called Paget’s disease (where bones become enlarged and deformed), or in certain cancers that spread to bone, ALP may be the only test result that is high.

Sometimes doctors don’t know why ALP is high, and they need to order other tests to determine the exact cause. In such cases, your doctor may order another enzyme, GGT, that is made by the liver in the same places as is ALP, but which is not made by bone.

PLEASE NOTE: Numerically reported test results are interpreted according to the test's reference range, which may vary by the patient's age, sex, as well as the instrumentation or kit used to perform the test. A specific result within the reference (normal) range – for any test – does not ensure health just as a result outside the reference range may not indicate disease. To learn more about reference ranges, please see the article, Reference Ranges and What They Mean. To learn the reference range for your test, consult your doctor or laboratorian. Lab Tests Online recommends you consult your physician to discuss your test results as a part of a complete medical examination.

Pregnancy can increase ALP levels. Children have higher ALP levels because their bones are growing, and ALP is often very high during the “growth spurt,” which occurs at different ages in males and females.

Eating a meal can increase the ALP level slightly for a few hours in some people. It is usually better to do the test after fasting overnight. Some drugs may increase ALP levels, especially some of the drugs used to treat psychiatric problems, but this is rare.

Fasting is preferred but not required for this test.