Alkaline Phosphatase (ALP)

Overview

What is alkaline phosphatase (ALP)?

Alkaline phosphatase (ALP) is an enzyme that’s found throughout your body. An enzyme is a type of protein in a cell that acts as a catalyst and allows certain bodily processes to happen. There are thousands of enzymes throughout your body that have important functions.

Even though researchers know the function of several other types of enzymes and have studied alkaline phosphatase for decades, they don’t yet know the exact function of ALP. However, researchers believe it’s important for multiple different processes.

ALP is often considered a liver enzyme because it’s primarily found in your liver. However, it also exists in the following places:

  • Your bile duct.
  • Your bones.
  • Your kidneys.
  • Your intestines.
  • The placenta in pregnant people.

Abnormal levels of ALP in your blood can reflect damage to tissue or disruption of normal bodily processes.

What is an alkaline phosphatase (ALP) blood test?

An alkaline phosphatase (ALP) test measures the amount of ALP in your blood. Although ALP exists throughout your body, the two main sources of ALP in your blood are your liver and bones. High levels of ALP may indicate liver disease or certain bone disorders, but an ALP test alone cannot diagnose a condition.

There are two main types of alkaline phosphatase (ALP) blood tests: a general ALP (the more common test) and an ALP isoenzyme test.

A general ALP test is usually included in a blood test known as a comprehensive metabolic panel (CMP) and a liver panel (HFP or LFT).

Whereas an ALP test just measures the level of ALP in your blood, an ALP isoenzyme test can differentiate between types of alkaline phosphatase based on where they originated in your body.

Your healthcare provider may have you undergo an ALP isoenzyme test as a follow-up if you had an abnormal ALP level on a previous test. While an isoenzyme test can provide more detailed information, it’s more technically challenging and expensive, and some laboratories may not offer it.

Why do I need an alkaline phosphatase blood test?

Your provider may order an alkaline phosphatase (ALP) blood test to help screen for, monitor or help diagnose liver and biliary diseases, bone disorders and other health conditions.

Screening means checking for potential health issues before you experience symptoms. An ALP test is often included in a comprehensive metabolic panel (CMP) and liver panel. Healthcare providers often use these panels as part of a routine check-up to screen for a wide range of potential health problems.

If you have a liver or bone condition or another type of condition, your provider may order an ALP test, often as part of a panel, to monitor your condition to see if it’s improving, worsening or staying the same with or without treatment.

Your provider may use an ALP test for diagnostic purposes when you have signs of possible liver or bone problems. An ALP test can also help diagnose the cause of more general symptoms, such as fatigue, when it’s included in a liver panel or CMP. While providers can’t diagnose a condition based solely on ALP levels, it can be an important part of the diagnostic process. The degree to which the ALP level is elevated or lower than usual may indicate the type or severity of a condition.

Signs and symptoms of liver disease include:

Signs and symptoms of bone disorders include:

How is an alkaline phosphatase (ALP) test different from a liver panel or comprehensive metabolic panel (CMP)?

A panel blood test involves more than one measurement from a blood sample. Because of this, a liver panel or comprehensive metabolic panel (CMP) provides more information than a test for just alkaline phosphatase. While you can undergo a blood test that just measures your ALP, it’s most often included in a panel with other measurements, such as liver enzymes, to get a more complete picture of your liver’s health.

Test Details

Who performs an alkaline phosphatase (ALP) blood test?

A healthcare provider called a phlebotomist usually performs blood draws, including those for an ALP blood test, but any healthcare provider who is trained in drawing blood can perform this task. The samples are sent to a lab where a medical laboratory scientist prepares the samples and performs the test on machines known as analyzers.

Do I need to fast for an alkaline phosphatase blood test?

If your alkaline phosphatase (ALP) test is part of a comprehensive metabolic panel (CMP), you’ll likely need to fast for 10 to 12 hours before your CMP blood test. Fasting means not eating or drinking anything other than water.

In any case, your healthcare provider will give you specific instructions when they order a blood test for you. Be sure to follow them.

What should I expect during my alkaline phosphatase (ALP) blood test?

You can expect to experience the following during a blood test, or blood draw:

  • You’ll sit in a chair, and a healthcare provider will check your arms for an easily accessible vein. This is usually in the inner part of your arm on the other side of your elbow.
  • Once they’ve located a vein, they’ll clean and disinfect the area.
  • They’ll then insert a small needle into your vein to take a blood sample. This may feel like a small pinch.
  • After they insert the needle, a small amount of blood will collect in a test tube.
  • Once they have enough blood to test, they’ll remove the needle and hold a cotton ball or gauze on the site to stop the bleeding.
  • They’ll place a bandage over the site, and you’ll be finished.

The entire procedure usually takes less than five minutes.

What should I expect after my alkaline phosphatase blood test?

After a healthcare provider has collected your blood sample, they’ll send it to a laboratory for testing. Once the test results are back, your healthcare provider will share the results with you.

What are the risks of an alkaline phosphatase (ALP) test?

Blood tests are a very common and essential part of medical testing and screening. There’s very little risk to having blood tests. You may have slight tenderness or a bruise at the site of the blood draw, but this usually resolves quickly.

When can I expect the results of my alkaline phosphatase (ALP) test?

In most cases, you should have your test results within one to two business days, though it could take longer.

Results and Follow-Up

What do the results of an alkaline phosphatase (ALP) blood test mean?

Blood test reports, including alkaline phosphatase (ALP) test reports, usually provide the following information:

  • The name of the blood test or what was measured in your blood.
  • The number or measurement of your blood test result.
  • The normal measurement range for that test.
  • Information that indicates if your result is normal or abnormal or high or low.

What is the normal range for alkaline phosphatase (ALP)?

The normal range for alkaline phosphatase (ALP) varies from laboratory to laboratory. One common reference range is from 44 to 147 international units per liter (IU/L), but some organizations recommend a range of 30 to 120 IU/L. Because of this, it’s important to check your test result report to see what your specific lab’s reference range is.

It’s also important to note that normal alkaline phosphatase levels vary with age and sex. ALP levels are typically elevated during childhood and puberty due to bone growth and development. Between the ages of 15 to 50 years, ALP levels are slightly higher in males than females. ALP levels then rise again in old age.

ALP levels may also be higher in pregnant people since ALP exists in the placenta and in people who are healing from a bone fracture (break).

What does it mean if my alkaline phosphatase (ALP) is high?

It’s important to note that elevated levels of ALP can range in severity. While a very high ALP level often means you have liver damage or a bone disorder, mildly elevated levels can be caused by many different factors — not necessarily a medical condition that needs treatment. If you only have a mild elevation in your ALP levels, your healthcare provider will likely not have you undergo extensive evaluation. Instead, they’ll likely monitor your levels over time to make sure they don’t get worse.

High alkaline phosphatase (ALP) levels may indicate that there’s damage to your liver or that you have a type of bone disorder. Liver damage creates a different type of ALP than bone disorders do. If your test results reveal that you have high ALP levels, your provider may have you undergo additional tests, such as an ALP isoenzyme test, to determine where the excess ALP is coming from.

High alkaline phosphatase levels in the liver may indicate the following conditions:

  • Cholestasis of pregnancy: This is a common liver disease that can develop late in pregnancy.
  • Cirrhosis of the liver: Cirrhosis is a late-stage liver disease in which healthy liver tissue is replaced with scar tissue and the liver is permanently damaged.
  • Hepatitis: Hepatitis is inflammation of the liver. There are many types of hepatitis.
  • Biliary atresia: This is a rare condition that happens when there’s a blockage in the tubes (ducts) that carry bile from your liver to your gallbladder. It occurs in infants.
  • Biliary stricture: This condition happens when the bile duct (the tube that takes bile from the liver to the small bowel) gets smaller or narrower.
  • Biliary obstruction due to cancer: Certain cancers, including cholangiocarcinoma and pancreatic head adenocarcinoma, can block your bile ducts or pancreatic ducts.
  • Mononucleosis (“mono”): This is a contagious infection that can sometimes cause swelling in your liver.

High bone alkaline phosphatase levels may indicate the following conditions:

  • Bone metastasis: This condition happens when cancer cells from elsewhere in your body spread to your bones.
  • Paget’s disease of the bone (osteitis derformans): This is a rare chronic bone disorder in which there is excessive breakdown and regrowth in the affected bone(s).
  • Osteogenic sarcoma: This is a type of cancer that starts in your bones.
  • Healing fractures.
  • Hyperparathyroidism: This condition happens when your parathyroid glands release too much parathyroid hormone, which causes calcium levels in your blood to rise.
  • Hyperthyroidism: This condition happens when your thyroid produces and releases too much thyroid hormone.
  • Osteomalacia: This is a disease that weakens your bones and can cause them to break more easily. It develops most commonly due to a vitamin D deficiency.

A high level of ALP may also be a sign of untreated celiac disease.

What does it mean if my alkaline phosphatase (ALP) is low?

Having an abnormally low level of alkaline phosphatase (ALP) is less common than having an elevated level. It may indicate the following conditions:

  • Malnutrition.
  • Zinc deficiency.
  • Magnesium deficiency.
  • Hypothyroidism.
  • Rare genetic conditions, including hypophosphatasia and Wilson disease.

Should I be concerned if I have high or low alkaline phosphatase (ALP) test results?

If your ALP test result is high or low, it doesn't necessarily mean that you have a medical condition that needs treatment. Other factors can affect your levels, including:

  • Certain medications, such as birth control pills.
  • Your diet.
  • Being pregnant.
  • Your age — teens and children may have higher levels because their bones are growing.
  • Having AIDS.
  • An error in the collection, transport or processing of the test.

Before determining if you need to undergo further tests, your healthcare provider will take into consideration many aspects of your health and situation, including:

  • Your medical history.
  • Your current medications.
  • How high or low your ALP results are.
  • The results of other tests usually taken alongside ALP.
  • If you’re experiencing symptoms.

When should I call my doctor?

If you’re experiencing symptoms of liver damage, such as jaundice, or bone disorders, such as bone or joint pain, call your healthcare provider. If you’ve been diagnosed with a liver condition or a bone disorder and are experiencing new or concerning symptoms, contact your provider.

If you have any questions about you’re alkaline phosphatase results, don’t be afraid to ask your provider questions.

A note from Cleveland Clinic

Seeing an abnormal test result can be stressful. Know that having a high or low level of alkaline phosphatase doesn’t necessarily mean you have a medical condition and need treatment. Approximately one in 20 healthy people have test results outside of the normal range. Your healthcare provider will let you know if you need to undergo further tests to determine the cause of the abnormal level. Don’t be afraid to ask your provider questions. They’re there to help you.

Last reviewed by a Cleveland Clinic medical professional on 11/04/2021.

References

  • Lab Tests Online. Alkaline Phosphatase (ALP). (https://labtestsonline.org/tests/alkaline-phosphatase-alp) Accessed 11/5/2021.
  • Lowe D, Sanvictores T, John S. Alkaline Phosphatase. StatPearls [Internet]. Treasure Island, FL: StatPearls Publishing; 2021. https://www.ncbi.nlm.nih.gov/books/NBK459201/. (https://www.ncbi.nlm.nih.gov/books/NBK459201/) Accessed 11/5/2021.
  • MedlinePlus. Alkaline Phosphatase. (https://medlineplus.gov/lab-tests/alkaline-phosphatase/) Accessed 11/5/2021.

Cleveland Clinic is a non-profit academic medical center. Advertising on our site helps support our mission. We do not endorse non-Cleveland Clinic products or services. Policy