What is Low Alkaline Phosphatase?

Low alkaline phosphatase levels are less common, but still severe

Low alkaline phosphatase (ALP) can be a sign of a number of different conditions, including thyroid disease, celiac disease, and malnutrition. 

ALP is an enzyme found in the blood that helps break down proteins. It plays a role in numerous processes in the human body, and any abnormalities in blood concentrations—either high or low—may indicate a health condition.

In adults, the normal range of alkaline phosphatase is 33 to 96 U/L, though what's considered "normal" may vary from laboratory to laboratory.

This article goes over low alkaline phosphatase and the conditions it's associated with. It also discusses how ALP testing is performed and interpreted.

Alkaline phosphatase test can be drawn in a serum separator tube
David Silverman / Getty Images

What Is Alkaline Phosphatase?

Alkaline phosphatase is an enzyme. An enzyme is a type of protein that catalyzes (causes or accelerates) chemical reactions in the body. ALP is produced mainly by the liver and bones but is also synthesized in smaller quantities by the intestines and kidneys. ALP is also secreted from the placenta during pregnancy.

Scientists have not yet identified the full range of biochemical reactions that ALP instigates, but the enzyme is known to contribute to the following processes:

  • Transporting nutrients and enzymes to and from the liver
  • Aiding in the development, growth, and maintenance of bone
  • Transporting calcium and phosphate from the intestines to bones, muscles, and nerve cells to ensure normal function
  • Transporting fatty acids to store energy in adipose tissues and help maintain the structural integrity of cells
  • Regulating cell growth in fetuses during pregnancy

ALP is found in all tissues of the body but, not surprisingly, is found in its highest concentration in the liver, bones, kidneys, and intestines as well as the bile ducts (that drain bile from the liver) and gallbladder (that stores bile).

Certain diseases or conditions can impair ALP synthesis and lead to a drop in blood concentration. By contrast, damage to organs such as the liver or kidneys can trigger an increase of ALP in the bloodstream.

What Are the Causes of Low Alkaline Phosphatase?

Abnormally low ALP values may be the result of:

Signs and Symptoms of Low Alkaline Phosphatase

When you have low alkaline phosphatase, you may experience a variety of symptoms depending on the underlying health condition that is causing your levels to be low. 

For example, if you have aplastic anemia you may experience frequent bruising and nosebleeds and shortness of breath during activities. If you have celiac disease, you may experience gastrointestinal symptoms such as diarrhea or constipation, bloating, gas, and abdominal pain. Other conditions will cause very different symptoms.

Low Alkaline Phosphatase vs. High Alkaline Phosphatase

It is more common to have high ALP levels than low ALP levels. High ALP levels can be a sign of a number of different conditions, including:

What is Alkaline Phosphatase Testing?

The ALP test measures the amount of alkaline phosphatase in a sample of blood. Your healthcare provider may order an ALP test as a part of a routine checkup. They may also order the test to help diagnose a suspected disease. The ALP is often done alongside other blood tests, since the ALP test alone can't be used to diagnose a condition.

How to Prepare for the Test

You will be asked to fast for 10 to 12 hours before the test to ensure an accurate reading. Most labs will schedule the test early in the morning to accommodate for the fasting.

There are certain drugs that can interfere with the results. Advise your healthcare provider or the lab if you take any of the following:

Your healthcare provider will tell you if you need to stop taking any of these medications before the test. Do not discontinue any medications unless your healthcare provider tells you to.

What Happens During the Test?

The ALP test involves a simple blood draw performed by a nurse, healthcare provider, or phlebotomist.

As with other blood tests, the healthcare provider will draw blood from a vein in your arm using a small needle. The blood will be placed in a vial and sent to a laboratory for analysis. The blood draw typically takes less than five minutes. You may feel a prick or sting when the needle is inserted.

Like other blood tests, there is very little risk in having an alkaline phosphatase level test. You may experience mild pain and bruising where the blood was drawn.

What Do the Results Mean?

Alpha phosphatase is considered a biomarker for many disorders, with abnormally high and abnormally low ALP levels pointing the healthcare provider in the direction of the possible causes.

The ALP test results are presented as a reference range of values measures in enzyme units per liter (U/L) or microkatals per liter (μkat/L). Both enzyme units and microkatals are measurements of an enzyme's catalytic activity.

The normal range of values of ALP differs by age and pregnancy status. ALP values are higher in children because their bones are actively growing, while the ALP values increase during pregnancy in tandem with the development of the placenta and the approach of childbirth.

  By U/L By μkat/L
Adults 33 to 96 U/L 0.55 to 1.6 μkat/L
Children Under 350 U/L Under 5.8 μkat/L
Pregnacy (first trimester) 17 to 88 U/L 0.28 to 1.47 μkat/L
Pregnacy (second trimester) 25 to 126 U/L 0.42 to 2.1 μkat/L
Pregnacy (third trimester) 38 to 229 U/L 0.63 to 3.8 μkat/L

ALP values that fall outside these reference ranges are considered abnormal. On their own, abnormal ALP values are not diagnostic but can provide a clue as to the underlying cause.

If your ALP levels are low, your healthcare provider may also order blood tests to look for hormone imbalances (such as occurs in thyroid or parathyroid disease), generalized inflammation, or genetic mutations.

Based on the results of these blood tests, a healthcare provider can expand the investigation and order the appropriate tests and procedures to definitively diagnose the cause.

What is the Treatment for Low Alkaline Phosphatase?

The treatment for low ALP depends on the underlying cause.

For example, if your low ALP levels are caused by malnutrition, they can be corrected by changing your diet so you're getting all of the nutrients your body needs. If they're caused by celiac disease, switching to a gluten-free diet will help. Other conditions, such as aplastic anemia, may require more aggressive treatment such as a bone marrow transplant.


Low alkaline phosphatase can be caused by a variety of conditions, including malnutrition, celiac disease, aplastic anemia, and others. It is more common to have high ALP levels than low levels.

Low alkaline phosphatase levels are found with an ALP blood test. An ALP blood test by itself isn't diagnostic, however. If your test shows low ALP levels, your healthcare provider will order other tests to see what is causing them.

Treatment for low alkaline phosphatase depends on the underlying cause.

Frequently Asked Questions

  • What is the normal range of alkaline phosphatase?

    Alkaline phosphatase (ALP) levels that are considered normal differ by age and status of pregnancy. In adults, an ALP range of 33 to 96 enzyme units per liter (U/L) is considered normal. For children, this range is under 350 U/L. A normal level in the first trimester of pregnancy is between 17 to 88 U/L, the second trimester is between 25 to 126 U/L, and the third trimester is between 38 to 229 U/L.

  • What causes a high level of ALP in a blood test?

    If blood test results show a high level of alkaline phosphatase (ALP), it could indicate liver damage or a bone disorder. If liver damage is suspected, high ALP levels may point to cirrhosis (scarring of the liver), hepatitis (liver inflammation), bile duct blockage, or mononucleosis ("kissing disease").

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Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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By James Myhre & Dennis Sifris, MD
Dennis Sifris, MD, is an HIV specialist and Medical Director of LifeSense Disease Management. James Myhre is an American journalist and HIV educator.