The alkaline phosphatase (ALP) test measures how much alkaline phosphatase you have in your blood. Alkaline phosphatase is an enzyme found throughout your body. But it is mainly in your liver, bone, kidney, and digestive tract.
You may need this test if you're at risk for a condition that affects your liver. For instance, your blood can show higher levels of ALP if one of the bile ducts that drains your liver becomes blocked. Conditions such as liver cancer, cirrhosis, and hepatitis can also cause ALP levels to rise. Bone disorders like Paget disease and healing fractures are other things that may affect your ALP levels. Younger children with high bone growth may also have higher ALP levels.
The ALP test may be done as part of a routine liver panel, a group of blood tests that looks at how well your liver is working.
If your ALP levels are too high, your healthcare provider may order an ALP isoenzyme test to find out what type of ALP is elevated in your blood. Liver disorders make different forms of ALP than bone disorders.
Test results may vary depending on your age, gender, health history, and other things. Your test results may be different depending on the lab used. They may not mean you have a problem. Ask your healthcare provider what your test results mean for you.
ALP results are reported in units per liter (U/L). For men and women older than age 18, an ALP level between 44 and 147 U/L is considered normal. The normal range for children is higher than that for adults, especially for infants and teens because their bones are growing rapidly.
The test is done with a blood sample. A needle is used to draw blood from a vein in your arm or hand.
Having a blood test with a needle carries some risks. These include bleeding, infection, bruising, and feeling lightheaded. When the needle pricks your arm or hand, you may feel a slight sting or pain. Afterward, the site may be sore.
Eating before the test may slightly increase your ALP levels for a few hours.
Pregnancy may cause higher levels of ALP. Teens, who often grow rapidly, tend to have higher ALP levels than people in other age groups.
You may need to fast—not eat or drink anything—for several hours before this test. You may be asked to stop taking any blood-thinning medicines before the test.
Be sure your healthcare provider knows about all medicines, herbs, vitamins, and supplements you are taking. This includes medicines that don't need a prescription and any illegal drugs you may use.