An alkaline phosphatase level test (ALP test) measures the amount of alkaline phosphatase enzyme in your bloodstream. The test requires a simple blood draw and is often a routine part of other blood tests.

Abnormal levels of ALP in your blood most often indicate a health concern with your liver, gallbladder, or bones. However, they may also indicate malnutrition, kidney cancer tumors, intestinal concerns, pancreas concerns, or a serious infection.

The normal range of ALP varies from person to person and depends on your age, blood type, gender, and whether you’re pregnant.

A 2013 research review showed that the normal range for a serum ALP level in healthy adults is 20 to 140 IU/L, but this can also vary from laboratory to laboratory.

The normal range runs higher in children and decreases with age.

The best way to know what is normal or not is to discuss the results with your doctor, who will be able to interpret the lab’s specific result and reference ranges.

What is alkaline phosphatase?

ALP is an enzyme found in your bloodstream. It helps break down proteins in the body and exists in different forms, depending on where it originates.

Your liver is one of the main sources of ALP, but some is also made in your bones, intestines, pancreas, and kidneys. In pregnant people, ALP is made in the placenta.

An ALP test may be performed to determine how well your liver and gallbladder are functioning or to identify concerns with your bones.

Liver and gallbladder

Checking ALP levels in the blood is a routine part of liver function and gallbladder tests. Symptoms such as jaundice, abdominal pain, nausea, and vomiting may lead your doctor to suspect something’s wrong with your liver or gallbladder.

The ALP test can be helpful in identifying conditions such as:

You may also need an ALP test if you’re taking a medication that has the potential to damage your liver, such as acetaminophen (Tylenol). Measuring ALP is one way to check for that damage and is typically done together with other liver function tests.

Bones

The ALP test can be helpful in the diagnosis of bone concerns such as:

  • rickets, a weakening or softening of the bones in children that’s most commonly due to a significant deficiency of vitamin D or calcium
  • osteomalacia, a softening of the bones in adults usually due to significant vitamin D deficiency, but also possibly due to the body’s inability to process and use vitamin D properly
  • Paget’s disease of the bone, a condition causing serious concerns with bone destruction and regrowth

ALP testing may also be helpful in investigating the presence of cancer tumors, unusual bone growth, or vitamin D deficiency. It can also be used to check the progress of treatment for any of the above conditions.

Having blood drawn for an ALP test is routine. It’s usually combined with other liver and kidney function tests.

You may have to fast for 10 to 12 hours before the test. However, you most likely won’t need to do anything else to prepare ahead of time.

If the results of the test are inconclusive, your doctor may order a follow-up test.

Eating can interfere with your ALP levels. Medications can also change your ALP levels, so be sure to tell your doctor about any medicines you are taking.

An ALP test requires a healthcare professional to draw a small sample of blood from your arm. This is done in your doctor’s office or in a clinical lab.

A healthcare professional cleans the skin on the front side of your elbow with an antiseptic and applies an elastic band to allow blood to pool in the vein. They then insert a needle into the vein to draw blood into a small tube. The process is quick and typically causes little pain or discomfort.

The blood sample is collected in a tube and analyzed by a laboratory. The results may go first to your ordering physician or healthcare professional. This typically takes 1 to 2 days. Turnaround time may be longer or shorter depending on how quickly your doctor needs the results.

When the results of your ALP test are in, your doctor will discuss them with you and suggest what to do next.

High levels

Higher-than-normal levels of ALP in your blood may indicate a health concern with your liver or gallbladder. This could include a blockage in your bile ducts, gallstones, cirrhosis, liver cancer, and some forms of hepatitis.

High levels may also indicate a concern related to the bones such as rickets, Paget’s disease, bone cancer, or an overactive parathyroid gland.

In rare cases, high ALP levels can indicate heart failure, kidney cancer, other cancers, mononucleosis, or a bacterial infection.

Low levels

Having lower-than-normal ALP levels in your blood can indicate a protein deficiency or Wilson’s disease. It may also signal malnutrition, which could be caused by celiac disease or an insufficient amount of certain vitamins and minerals.

Low ALP can also indicate a rare condition called hypophosphatemia. This causes fragile bones that can easily fracture and are slow to heal.

Interpreting the results

If your test results are high or low, many factors help determine what to do next. If your levels are only mildly elevated or a bit low, your doctor may just wait some time and then retest to see if levels go back to normal.

Your doctor also considers:

  • Other test results. As an ALP test is often done as part of a panel, your doctor will take into account measurements such as other enzyme levels.
  • Your current overall health. If you have symptoms that still need explaining, or point to a diagnosis, your doctor will use these to interpret your ALP results.

ALP tests are generally accurate, but they only show part of the picture. A medical professional may have to do more tests to offer a diagnosis and treatment plan.

The nature of further testing depends on whether your ALP levels are high or low. Your doctor may want to find the source of high ALP levels, or explain why ALP is low. Follow-up tests might include:

  • isoenzyme tests (to determine levels from the liver and bones)
  • diagnostic imaging of liver and gall bladder
  • vitamin and mineral levels
  • organ function tests

Your doctor can work with you to uncover why your ALP test results are out of range, and whether that’s a cause for concern.

There are very few risks associated with having your blood drawn.

You may experience some bruising around the puncture site, but this can be avoided by putting pressure on the wound.

In rare cases, phlebitis (inflammation of the vein) may develop. If you experience this complication, apply a warm compress until the swelling goes down.

Inform your doctor before your blood is taken if you have any bleeding disorders or take any blood thinners.

An alkaline phosphatase level test (ALP test) is a simple test to perform. It requires just a simple blood draw. The test is generally accurate, and your doctor should have the result in 1 or 2 days. Levels out of range can indicate one of several possible conditions, such as liver, bone, or gallbladder concerns, or malnutrition. Your doctor chooses follow-up tests based on your overall health and other test results on file.