The alkaline phosphatase (ALP) test measures the level of alkaline phosphatase in your blood. Alkaline phosphatase is an enzyme found throughout the body but is mainly in the 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 elevated 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's disease and healing fractures, are other factors that may affect your 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 doctor 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.
Many things may affect your lab test results. These include the method each lab uses to do the test. Even if your test results are different from the normal value, you may not have a problem. To learn what the results mean for you, talk with your health care provider.
ALP results are reported in units per liter (U/L). For men and women older than 18, an ALP level between 37 and 116 U/L is considered normal.
The general ranges for children and teens are:
1-3 years: 104-345 U/L
4-6 years: 93-309 U/L
7-9 years: 86-315 U/L
10-12 years: 42-362 U/L
13-15 years: 74-390 U/L
16-18 years: 52-171 U/L
1-3 years: 108-317 U/L
4-6 years: 96-297 U/L
7-9 years: 69-325 U/L
10-12 years: 51-332 U/L
13-15 years: 50-162 U/L
16-18 years: 47-119 U/L
The test requires a blood sample, which is drawn through a needle from a vein in your arm.
Taking a blood sample with a needle carries risks that include bleeding, infection, bruising, or feeling dizzy. When the needle pricks your arm, you may feel a slight stinging sensation or pain. Afterward, the site may be slightly 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 – before this test. You may be asked to stop taking any blood-thinning medications before the test.
Also be sure your doctor knows about all medicines, herbs, vitamins, and supplements you are taking. This includes medicines that don't need a prescription and any illicit drugs you may use.