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  • Also Known As:
  • ALP
  • ALP
  • Isoenzyme Test
  • ALP Fractionation Test
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Test Quick Guide

Alkaline phosphatase (ALP) is an enzyme that is present in many parts of the body, but it is primarily found in the liver, bones, intestine, and kidneys.

Alkaline phosphatase testing measures the amount of this enzyme in the blood. Abnormal levels of ALP can be caused by liver problems and other types of health problems.

ALP can be tested alone, but because many conditions can affect ALP levels, it is common to test ALP alongside other enzymes, such as in a liver panel test, in order to obtain more information about the most likely cause of abnormal results. An ALP isoenzyme test can identify the part of the body where ALP in the blood originated, but this type of testing is complex and not widely available.

About the Test

Purpose of the test

The purpose of testing alkaline phosphatase is to determine if you have normal levels of this enzyme. An ALP blood test can be used for screening, diagnosis, and monitoring of liver diseases and other health conditions.

Screening is checking for health problems before any symptoms have occurred. Screening tests rarely measure ALP alone, but it is a standard part of multi-measurement tests such as a liver panel and comprehensive metabolic panel (CMP). These tests may be prescribed as part of a routine check-up to screen for a range of potential health problems.

Diagnosis is the process of finding the cause after symptoms have developed. ALP is most often tested for diagnosis when there are signs of possible liver problems, such as nausea and vomiting, jaundice, fatigue, abdominal pain, or unexplained weight loss. It is also often prescribed if you have symptoms of a possible bone disorder such as bone pain, susceptibility to bone fractures, or abnormal bone shape. For general symptoms, ALP measurement as part of a liver panel or CMP may help identify the cause.

While ALP levels alone are not sufficient to diagnose an underlying condition, they can be an important part of the diagnostic process. The degree of ALP elevation may reflect the type or severity of a condition. An ALP isoenzyme test to measure specific kinds of ALP can help determine the part of the body affected and help diagnose the problem.

Monitoring is tracking the course of a health condition or your response to treatment. An ALP test, often as part of a panel, may be used to see if liver disease or other conditions are improving, worsening, or staying the same.

What does the test measure?

This test measures alkaline phosphatase, which is a type of enzyme. The typical measurement for this test is international units per liter (IU/L), a standardized measurement utilized by most laboratories that is based on the biological activity of ALP.

The exact function of ALP in the body is not fully understood, but researchers believe it to be important to multiple different processes. ALP can be found in the liver, bones, placenta of pregnant women, intestine, kidneys, and in other parts of the body. Abnormal levels in the blood can reflect damage to tissue or disruption of normal processes in the body.

Another type of ALP testing is an ALP isoenzyme or ALP fractionation test. In this test, specific subtypes of ALP are measured. These subtypes indicate where in the body the ALP was produced. While this testing can be beneficial, it is technically challenging and therefore much less common than general ALP testing.

When should I get an alkaline phosphatase test?

When ALP is tested, it is most often part of a panel test that includes other measurements that can reflect liver and kidney health. For example, the liver panel and comprehensive metabolic panel may measure ALP as part of a routine check-up or if you have symptoms that could be caused by liver or kidney conditions.

Testing for ALP alone may be conducted when you have symptoms of a problem affecting your liver or bones. It may also help monitor your response to treatment for liver or bone diseases.

ALP isoenzyme tests are most common as a follow-up after finding abnormal levels of ALP on a prior test.

Because testing for ALP can be used in many different medical contexts, a physician can best determine when it should be prescribed.

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Finding an Alkaline Phosphatase Test

How to get tested

ALP tests are normally prescribed by a doctor. They may recommend a blood test for ALP alone, but in most cases ALP will be included among several measurements on a panel test. Testing requires a blood draw that is typically done in a medical office, hospital, or laboratory.

Can I take the test at home?

At-home alkaline phosphatase testing is not widespread, but some at-home options are available to measure ALP as part of a liver panel. In these tests, you take a blood sample with a fingerstick and then send that sample to a laboratory where it can be analyzed.

Alkaline phosphatase isoenzyme tests are generally not available with at-home test kits.

How much does the test cost?

The price for ALP testing can vary based on where you live, the location where you have your blood sample taken, whether ALP is tested alone or with other measurements, and whether you have health insurance. Costs for ALP isoenzyme testing may be different than costs for standard ALP tests.

Technician fees for the blood draw, laboratory fees, and charges for office visits can all be included in the cost of an ALP test. Health insurance often covers most or all of these costs when the test is prescribed by your doctor, but you may need to pay a deductible or copay.

At-home tests are not covered by insurance and may be available for less than $150.

For details about what your out-of-pocket costs would be for alkaline phosphatase tests, check directly with your doctor’s office and your health insurance provider.

Taking an Alkaline Phosphatase Test

Alkaline phosphatase tests, including ALP isoenzyme tests, are usually done with a sample of blood that is taken from a vein in your arm. The blood sample can be taken in a health clinic, medical office, laboratory, or a similar setting.

For an at-home test, you can obtain a sample with a fingerstick and then send that by mail to a medical lab.

Before the test

Test preparations can depend on the specifics of the test being performed and the requirements of the laboratory that will analyze your sample:

  • Tests of ALP alone don’t always require fasting, but some laboratories may request that you not eat any food or drink anything other than water for 6-12 hours before the test.
  • When ALP is tested as part of a panel, it is common for fasting to be required.
  • ALP isoenzyme tests also usually require fasting.

You may also be asked about any medications or supplements that you take, and your doctor will advise you if you need to adjust the timing or dosage of these before the test.

For at-home tests, you should carefully consult any instructions provided by the test kit to find out if any special preparations are required.

During the test

For standard ALP tests, a sample of blood will be drawn from your arm. An elastic band will be placed around your upper arm to increase blood flow through your veins. A technician will use an antiseptic wipe on the underside of your arm near the elbow, and a needle will be inserted into the vein to withdraw a small vial of blood.

The blood draw is usually complete within a couple of minutes. There may be a brief sting when the needle is inserted and removed.

For an at-home test, materials and instructions will be included in the test kit. You will need to clean your fingertip with an antiseptic and then prick it with a small needle to obtain a drop of blood that is applied to the provided test paper. That test paper must then be prepared to be sent by mail to the lab. Make sure to follow any instructions to ensure proper at-home sample collection.

After the test

After your blood draw is finished, a cotton swab or bandage will be applied to apply pressure and stop any continued bleeding. Serious effects are uncommon, but there may be tenderness in your arm. Some bruising around the puncture site is also possible.

You can return to driving and most normal activities once the test is complete. If you were required to fast, you may want to bring something to eat after the test is finished.

For an at-home test, you usually will not have lasting pain or bleeding, but a bandage can be applied if your fingertip keeps bleeding.

Alkaline Phosphatase Test Results

Receiving test results

ALP test results are normally available within a few business days after the lab receives your sample. Your test report may be sent in the mail or electronically. Your doctor’s office may also contact you to share your test results.

Receiving results may take a few extra days for at-home tests because your test sample has to be sent by mail to the laboratory. The test report is normally accessible online or with a smartphone app, although you may also be contacted by a health professional that works for the at-home testing company.

Interpreting test results

Your test report will show your measured alkaline phosphatase level, which is usually reported in international units per liter (IU/L). The report may also list a reference range, which can vary from laboratory to laboratory. One common reference range is from 44 to 147 IU/L, but some professional organizations recommend a range of 30-120 IU/L. For this reason, it’s important to check your test report for the reference range of the lab that analyzed your sample.

Elevated ALP can be indicative of liver or bone diseases as well as many other types of conditions. However, high ALP levels are not always a sign of a problem. Interpretation of your test results can involve consideration of multiple factors:

  • The degree of elevation: Very high levels are often seen with blockages of the bile ducts, but high levels alone cannot distinguish between liver problems and other conditions.
  • Other test measurements: ALP is often measured along with other enzymes, such as aspartate aminotransferase (AST), alanine aminotransferase (ALT), gamma-glutamyl transpeptidase (GGT), and/or 5′-nucleotidase (5’-NT), and the levels of ALP relative to these enzymes can help determine the significance of your test result.
  • Your overall health: Any symptoms that you are experiencing will be considered alongside your ALP levels.

Your doctor can account for the fact that ALP levels can be elevated without any underlying illness. For example, ALP is usually higher in pregnant women, growing children and adolescents, and older adults. ALP produced in the intestine can also increase after fatty meals in people with certain blood types.

Abnormally low ALP levels are less common but can occur as a result of malnutrition, nutrient deficiencies, hypothyroidism, and some rare inherited disorders that affect ALP or liver function. Persistently low levels of ALP could indicate hypophosphatasia (HPP), a rare genetic disorder of bone metabolism.

If you have ALP isoenzyme testing, your test report will show levels for different types of ALP. Elevations of specific sources of ALP can identify the location of tissue damage or other disease in the body.

Regardless of the type of ALP test that you take, it is important to discuss your test results with your doctor who can best explain what they mean for your health and whether any other testing would be beneficial.

Are test results accurate?

ALP test results are usually regarded as accurate, but, like any medical test, an ALP blood test is not perfect. There are potential sources of error in the processing and analysis of your blood sample, so laboratories must take care to follow best practices to ensure dependable results.

Testing for ALP isoenzymes is more technically demanding. Different methods exist for determining the part of the body that is the source of increased ALP, but special techniques that are not available at all laboratories can make this testing much more reliable.

Do I need follow-up tests?

Follow-up tests of different kinds are common if your test shows abnormal levels of ALP. If ALP is only mildly elevated, you may have repeat blood testing after a period of time to see whether your ALP levels have returned to normal.

If ALP levels show more significant elevation, additional testing may be needed to determine where this ALP originated in the body. ALP isoenzyme tests or panel tests of multiple liver enzymes can provide evidence of the most likely source of excess ALP.

Depending on the origin on ALP, further tests may be prescribed. These can include laboratory tests to evaluate organ function, imaging tests, examinations of the bones or the liver and digestive system, and, when appropriate, biopsies or other diagnostic procedures.

Low levels of ALP may also require further testing to detect nutrient deficiency or other health problems that can interfere with the normal production of this enzyme.

The choice of follow-up testing depends on your ALP levels and how they compare to other measurements taken on panel tests. Your doctor also considers your symptoms, health history, and any other tests that have already been done when recommending next steps in your medical care. Reviewing your ALP test report with your doctor can help you understand which tests are most appropriate in your situation.

Questions for your doctor about test results

As you discuss your test report with your doctor, these questions may help you better understand your situation and most appropriate next steps in your care:

  • What did the test show about my ALP levels?
  • Were any other measurements taken in addition to ALP? What can you learn from those measurements?
  • Do you recommend any other tests? What are the pros and cons of different follow-up tests?

Related Tests

Not all ALP testing is the same, so it is common to have questions about how different tests are related. The following sections explain some important similarities and differences among tests that measure ALP.

How is an ALP test different from a liver panel or comprehensive metabolic panel?

A panel test involves more than one measurement, and for this reason, a liver panel or comprehensive metabolic panel is more extensive than a test for ALP alone. While ALP can be measured independently, it is most often included in a panel with other compounds, such as liver enzymes.

How is an ALP test different from an ALP isoenzyme test?

General ALP tests and ALP isoenzyme tests both measure alkaline phosphatase in the blood. The key difference is that an ALP isoenzyme test utilizes methods that can differentiate between types of ALP based on where they originated in the body.

ALP isoenzyme tests may be prescribed as a follow-up after an abnormal ALP level was found on a previous test. While an isoenzyme test can provide more detailed information, it is more technically challenging and may not be offered by some laboratories.

View Sources

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Friedman LS. Enzymatic measures of cholestasis (eg, alkaline phosphatase, 5′-nucleotidase, gamma-glutamyl transpeptidase). In: Chopra S, ed. UpToDate. Updated September 11, 2020. Accessed May 10, 2021. https://www.uptodate.com/contents/enzymatic-measures-of-cholestasis-eg-alkaline-phosphatase-5-nucleotidase-gamma-glutamyl-transpeptidase

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