What Is an ALP (Alkaline Phosphatase) Blood Test?

ALP Blood Test Overview

Doctors order ALP tests when you show signs or symptoms of liver or bone disease.
Doctors order ALP tests when you show signs or symptoms of liver or bone disease.

Enzymes are substances that cause different chemical reactions inside your body. For example, digestive enzymes break down food into molecules that your gut can absorb. 

Alkaline phosphatase (ALP) is one of your body’s enzymes. Many organs rely on ALP. It does different things for each of them. The two main sources of ALP in your blood are the liver and bone. An ALP test is part of routine blood work. So doctors often find high ALPs by accident in someone who isn’t having any symptoms. Your doctor may also order an ALP test if she is worried about a liver, gallbladder, or bile duct disease. Bile ducts are pipes that transport fluids that aid in digestion.  

What follows is information you need for a more complete understanding of what an ALP test is and what the results could mean for your health.

What Are Normal ALP Levels?

Normal adult ALP levels range from 20 to 140 international units per liter of blood, or IU/L.

ALP levels tend to soar during childhood when bones are growing and developing. So doctors don’t usually look at ALP levels when diagnosing problems in kids.

How Do Doctors Perform an ALP Test?

It’s a blood test. Usually, someone will take blood from a vein in your arm or hand. The blood is then analyzed in a lab and the results are reported to your doctor.

What Is the ALP Test For?

Doctors order an ALP test as part of routine blood work or when you show signs or symptoms of liver or bone disease. In liver disease, a noticeable increase in ALP suggests you have a reduced or blocked flow of bile. That’s a condition that doctors call cholestasis. When ALP is elevated in liver disease, it can be suggestive of obstructing gallstones or bile obstruction from cancer. Other things that can increase ALP levels include:

  • Medications
  • Infections that target the liver or biliary tract
  • Autoimmune diseases that involve the liver
  • Infiltrative liver disease like sarcoidosis or amyloidosis
  • Cancers that have spread to the liver
  • Bile duct stricture (or narrowing)
  • Lymphoma 

What these all have in common is obstruction of bile flow which will result in higher bilirubin levels and high ALP levels on liver tests

ALP is also increased in the setting of medical problems that cause increased bone turnover, meaning increased bone resorption and formation. 

Some examples include:

Problems that cause ALP levels to fall include:

  • Protein deficiency
  • Poor nutrition
  • Wilson disease

What Are Symptoms That Lead to an ALP Test?

Doctors usually check your ALP levels, along with other liver tests, if you have yellow skin (jaundice) -- a sign of bile duct blockage. Your doctor may also order an ALP test if you have some of the following symptoms:

But again, a wide variety of medical issues can cause ALP levels to rise or fall. Your doctor may order an ALP test in order to narrow down or rule out some of the possible causes of your symptoms. 

How Do You Prepare for the ALP Test?

You don’t need to do anything to prepare. Doctors can check ALP at any time of day. But some medications can interfere with the ALP test results. Make sure your doctor knows what you’re taking. You may have to stop using one or more of these medications just before taking the test. But don’t stop taking your meds unless your doctor says that you should.

Does the ALP Test Come With Risks?

This test comes with the same risks as any blood test. You might feel pain where the health care provider inserts the needle. If you are older or taking blood thinners, or if the vein is hard to find, you might get a bruise.

Are There Follow-Up Tests?

Your body contains different types of ALP. These different types perform different jobs. 

If you test high for ALP, your doctor may order follow-up testing to figure out whether the high ALP is from a bone or a liver problem. This can help the doctor zero in on your medical issue.

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Cleveland Clinic: “Elevated Liver Enzymes.”

Mayo Clinic: “Elevated Liver Enzymes: Symptoms.”

Labtestsonline.org: “Alkaline Phosphatase (ALP).”

University of California San Francisco Benioff Children’s Hospital: “ALP (Alkaline Phosphatase) Isoenzyme.”

University of California San Francisco Health: “ALP (Alkaline Phosphatase) Isoenzyme.”