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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 (such as Paget's disease or cancer that has spread to the bones), a disease that affects how much calcium is in the blood (hyperparathyroidism), vitamin D deficiency, or damaged liver cells.
If the ALP level is high, more tests may be done to find the cause. The amounts of different types of ALP in the blood may be measured and used to determine whether a high level is from the liver or bones. This is called an alkaline phosphatase isoenzymes test.
Why It Is Done
The ALP test is done to:
- Check for liver damage when you're taking medicines that can damage the liver.
- Help look for liver disease. Liver disease may cause symptoms. These may include pain in the upper belly, nausea, vomiting, and sometimes jaundice.
- Check for bone problems (sometimes found on X-rays). Some examples are rickets, osteomalacia, bone tumours, and Paget's disease. The test can also check for too much parathyroid hormone. This is the hormone that controls bone growth.
- Check to see how well treatment for Paget's disease or a vitamin D deficiency is working.
How To Prepare
- 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 you eat fatty foods.
- Tell your doctor ALL the medicines and natural health products you take. Some may increase the risk of problems during your test. Your doctor will tell you if you should stop taking any of them before the test and how soon to do it.
How It Is Done
A health professional uses a needle to take a blood sample, usually from the arm.
How long the test takes
The test will take a few minutes.
How It Feels
When a blood sample is taken, you may feel nothing at all from the needle. Or you might feel a quick sting or pinch.
There is very little chance of having a problem from this test. When a blood sample is taken, a small bruise may form at the site.
Each lab has a different range for what's normal. Your lab report should show the range that your lab uses for each test. The normal range is just a guide. Your doctor will also look at your results based on your age, health, and other factors. A value that isn't in the normal range may still be normal for you.
- Very high levels of ALP can be caused by liver problems, such as hepatitis, blockage of the bile ducts (obstructive jaundice), gallstones, cirrhosis, liver cancer, or cancer that has spread (metastasized) to the liver from another part of the body.
- High ALP levels can be caused by bone diseases, such as Paget's disease, osteomalacia, rickets, bone tumours, or tumours that have spread from another part of the body to the bone, or by overactive parathyroid glands (hyperparathyroidism). Normal healing of a bone fracture can also raise ALP levels.
- Heart failure, heart attack, mononucleosis, or kidney cancer can raise ALP levels. A serious infection that has spread through the body (sepsis) can also raise ALP levels.
- Women in the third trimester of pregnancy have high ALP levels because the placenta makes ALP.
Low levels of ALP can be caused by:
- Conditions that lead to malnutrition, such as celiac disease.
- A lack of nutrients in the diet.
- An inherited bone disease called hypophosphatasia.
Current as of: September 8, 2022
Author: Healthwise Staff
E. Gregory Thompson MD - Internal Medicine
Kathleen Romito MD - Family Medicine
Alan C. Dalkin MD - Endocrinology
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