Alkaline Phosphatase (ALP)

Alkaline phosphatase (ALP) is an enzyme. This is a protein that helps cells work. You find ALP in high concentrations in the cells that make bone and in the liver. Smaller amounts of ALP are found in the afterbirth (placenta) of women who are pregnant and in the bowel. Each of these body parts makes different forms of ALP. The different forms are called isoenzymes.

When a person has evidence of liver disease, very high ALP levels can tell your caregiver that the person's bile ducts are somehow blocked. Often, ALP is high in people who have cancer that has spread to the liver or the bones. Caregivers 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 caregiver is not sure why, he or she may also order ALP isoenzyme tests to try to determine the cause.

Pregnancy can increase ALP levels. Children have higher ALP levels because their bones are growing. 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. However, this is rare.


A blood sample is taken by needle from a vein in the arm. Fasting is preferred but not required for this test.


  • Elderly: slightly higher than adult

  • Adult: 30 to 120 units/L or 0.5 to 2 microKat/L (SI units)

  • Child, Less than 2 years: 85 to 235 units/L

  • Child, 2 to 8 years: 65 to 210 units/L

  • Child or Adolescent, 9 to 15 years: 60 to 300 units/L

  • Adolescent or Adult, 16 to 21 years: 30 to 200 units/L

Ranges for normal findings may vary among different laboratories and hospitals. You should always check with your caregiver after having lab work or other tests done to discuss the meaning of your test results and whether your values are considered within normal limits.


Your caregiver will go over the test results with you and discuss the importance and meaning of your results, as well as treatment options and the need for additional tests if necessary.


It is your responsibility to obtain your test results. Ask the lab or department performing the test when and how you will get your results.