An alkaline phosphatase (ALP) test measures the amount of the enzyme ALP in the blood. ALP is made mostly in the liver and in bone with some made in the intestines and kidneys. It also is made by the placenta of a pregnant woman.

The liver makes more ALP than the other organs or the bones. Some conditions cause large amounts of ALP in the blood. These conditions include rapid bone growth (during puberty), bone disease (osteomalacia or Paget's disease), or a disease that affects how much calcium is in the blood (hyperparathyroidism), or damaged liver cells.

If ALP is high, more tests may be done to find the cause.

Why It Is Done

A test for alkaline phosphatase (ALP) is done to:

• Check for liver disease or damage to the liver. Symptoms of liver disease can include jaundice, belly pain, nausea, and vomiting. An ALP test may also be used to check the liver when medicines that can damage the liver are taken.
• Check bone problems (sometimes found on X-rays), such as rickets, osteomalacia, bone tumors, Paget's disease, or too much of the hormone that controls bone growth (parathyroid hormone). The ALP level can be used to check how well treatment for Paget's disease is working.
• Check the cause of a high blood calcium level.

How To Prepare

An alkaline phosphatase test is often done at the same time as a routine blood test. You do not need to do anything before having a routine blood test.

If you are having a follow-up ALP test, you may be asked to not eat or drink for 10 hours before the test. The ALP level generally goes up after eating, especially after eating fatty foods.

Many medicines may change the results of this test. Be sure to tell your doctor about all the nonprescription and prescription medicines you take.

Talk to your doctor about any concerns you have regarding the need for the test, its risks, how it will be done, or what the results will mean. To help you understand the importance of this test, fill out the medical test information form(What is a PDF document?).

How It Is Done

The health professional drawing your blood will:

• Wrap an elastic band around your upper arm to stop the flow of blood. This makes the veins below the band larger so it is easier to put a needle into the vein.
• Clean the needle site with alcohol.
• Put the needle into the vein. More than one needle stick may be needed.
• Attach a tube to the needle to fill it with blood.
• Remove the band from your arm when enough blood is collected.
• Pur a gauze pad or cotton ball over the needle site as the needle is removed.
• Put pressure to the site and then a bandage.