Alkaline Phosphatase (ALP) | Healthmatters.io (2025)

What is Alkaline phosphatase (ALP)?

Alkaline phosphatase (ALP) is an enzyme (= enzymes are proteins that act as biological catalysts by accelerating chemical reactions) found in the blood that helps break down proteins and that plays a role in numerous processes in the human body. Any abnormalities in blood concentrations (either high or low) may be indicative of diseases ranging from gallstones and thyroid disease to hepatitis and cancer.

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).

Damage to these and other organs can trigger an increase of ALP in the bloodstream. By contrast, certain diseases or conditions can impair ALP synthesis and lead to a drop in the blood concentration.

What are the functions of ALP?

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

1. Transporting:

• nutrients and enzymes to and from the liver
• calcium and phosphate from the intestines to bones, muscles, and nerve cells to ensure normal function
• fatty acids to store energy in adipose tissues and help maintain the structural integrity of cells

2. Aiding in the development, growth, and maintenance of bone

3. Regulating cell growth in fetuses during pregnancy

Where is ALP produced?

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.

What is the ALP test?

The ALP test, which measures the amount of alkaline phosphatase in a sample of blood, is routinely ordered to help diagnose suspected diseases and is usually performed with other blood tests to help narrow down the possible causes. ALP is made mostly in the liver and in bone with some made in the intestines and kidneys. It also is made by the placenta of a pregnant woman.

ALP can be tested alone, but because many conditions can affect ALP levels, it is common to test it alongside other enzymes, such as in a liver panel test, 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 testing is complex and not widely available.

The purpose of testing ALP 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 or bone diseases and other health conditions.

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. ALP measurement as part of a liver panel or CMP (= Comprehensive Metabolic Panel) may help identify the cause of general symptoms.

While ALP levels alone are insufficient 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.

The typical measurement for this test is international units per liter (IU/L), a standardized measurement utilized by most laboratories based on the biological activity of ALP.

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

→ blockage of bile ducts (from a gallstone, inflammation, or cancer)

→ cholecystitis (inflammation of the gallbladder)

→ cirrhosis (scarring of the liver)

→ some forms of hepatitis (inflammation of the liver)

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).

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.

Drugs can interfere with results:

There are certain drugs that can interfere with the results. If your ALP levels are modestly raised, it may be due to the drugs you are taking rather than an underlying disease or medical condition.

Advise your healthcare provider or the lab if you take any of the following:

• Anabolic steroids
• Antibiotics, including penicillins and sulfonamides
• Anti-epilepsy drugs like Dilantin (phenytoin) and phenobarbital
• Antihypertensives like Verelan (verapamil), captopril, and methyldopa
• Birth control pills and other hormonal contraceptives
• Cortisone
• Hormone-replacement therapy, including estrogen and testosterone
• Monoamine oxidase inhibitors (MAOIs)
• Nonsteroidal anti-inflammatory drugs (NSAIDs) like aspirin, Advil (ibuprofen), Aleve (naproxen), and Celebrex (celecoxib)
• Inderal LA (Propranolol)
• Chlorpromazine
• Tricyclic antidepressants
• Zyloprim (allopurinol)
• Zyrtec Allergy (cetirizine)

Your ALP results:

Your test report will show your measured ALP level, 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 39 - 117 IU/L. For this reason, it’s important to check your test report for the lab’s reference range that analyzed your sample. The normal range runs higher in children and decreases with age.

Normal levels of ALP:

Adults: 39 to 117 IU/L

Children: Under 350 U/L

Pregnancy (first trimester): 17 to 88 U/L

Pregnancy (second trimester): 25 to 126 U/L

Pregnancy (third trimester): 38 to 229 U/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.

References:

Verma J, Gorard DAPersistently elevated alkaline phosphataseCase Reports 2012;2012:bcr2012006768.

Sharma, U., Pal, D. & Prasad, R. Alkaline Phosphatase: An Overview. Ind J Clin Biochem 29, 269–278 (2014). https://doi.org/10.1007/s12291-013-0408-y

Brichacek AL, Brown CM. Alkaline phosphatase: a potential biomarker for stroke and implications for treatment. Metab Brain Dis. 2019 Feb;34(1):3-19. doi: 10.1007/s11011-018-0322-3. Epub 2018 Oct 4. PMID: 30284677; PMCID: PMC6351214.

Links:

https://medlineplus.gov/lab-tests/alkaline-phosphatase

https://www.testing.com/tests/alkaline-phosphatase-alp/

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