Alkaline phosphatase: what is it, tests, interpretation


Alkaline phosphatase (ALP) is an enzyme found in the blood that helps break down proteins. ALP plays a role in many processes in the human body, and any deviation in blood concentration, high or low, can indicate a variety of diseases, from gallstones and thyroid diseases to hepatitis and cancer .

The ALP test, which measures the amount of alkaline phosphatase in a blood sample, is generally prescribed to help diagnose suspicious diseases and is usually done with other blood tests to help identify possible causes.

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What is alkaline phosphatase?

Alkaline phosphatase is an enzyme. An enzyme is a type of protein that catalyzes (triggers or speeds up) chemical reactions in the body. ALP is produced primarily by the liver and bones, but in smaller amounts it is synthesized by the intestines and kidneys . ALP is also excreted from the placenta during pregnancy.

Scientists have not yet identified the full range of biochemical reactions that cause ALP, but this enzyme is known to be involved in the following processes:

  • Transport of nutrients and enzymes to and from the liver.
  • Helps in the development, growth and maintenance of bones.
  • Transport of calcium and phosphate from the intestine to bones, muscles and nerve cells for normal function.
  • Transport fatty acids for energy storage in adipose tissue and maintain the structural integrity of cells.
  • Regulation of cell growth in the fetus during pregnancy.

ALP is found in all tissues of the body, but unsurprisingly in the highest concentration in the liver, bones, kidneys, and intestines, as well as in the bile ducts (which drain bile from the liver) and the gallbladder (which stores bile). ).

Damage to these and other organs can lead to increased levels of ALP in the bloodstream. On the contrary, certain diseases or conditions can interfere with the synthesis of ALP and cause a decrease in blood concentration.

ALP test

Alkaline phosphatase is usually tested if liver, bone, gallbladder, kidney, or intestinal disease is suspected.

This is especially true for liver disease, in which inflammation of the liver (called hepatitis ) often presents with jaundice (yellowing of the skin and eyes), fatigue, upper abdominal pain, nausea and vomiting, dark urine, and clay-colored stools

ALP tests play an important role in diagnosing liver disease. Similar symptoms can occur with gallbladder diseases.

For bone disease, the ALP test is usually done if a person has chronic bone pain , unexplained fractures , or enlarged or irregular bones.

An ALP test involves a simple blood draw performed by a nurse, doctor, or phlebotomist . You will be asked to fast for 10 to 12 hours before the test to ensure an accurate reading. Most labs schedule an early morning test to accommodate fasting.

There are certain medications that can affect the results. Tell your doctor or laboratory if you are taking any of the following:

If your ALP level is slightly elevated, it may be related to the medications you are taking and not an underlying medical or health condition.


Alpha phosphatase is considered a biomarker for many diseases, with abnormally high and abnormally low ALP levels indicating possible causes.

The results of the ALP test are presented as a reference range of values, measured in units of enzymes per liter (U / L) or microcatals per liter (μkat / L). Both enzyme units and microcatals are indicators of the catalytic activity of an enzyme.

The normal range of ALP values differs according to age and the stage of pregnancy. ALP values are higher in children, because their bones are actively growing, while ALP values increase during pregnancy, simultaneously with the development of the placenta and the onset of labor.

Author: U / L Author: μkat / L
Adults From 33 to 96 U / l 0.55 to 1.6 μkat / L
Kids Less than 350 U / l Less than 5.8 μkat / L
Pregnancy (first trimester) From 17 to 88 U / l 0.28 to 1.47 μkat / L
Pregnancy (second trimester) From 25 to 126 U / l 0.42 to 2.1 μkat / L
Pregnancy (third trimester) From 38 to 229 U / l 0.63 to 3.8 μkat / L

ALP values outside of these reference ranges are considered abnormal. By themselves, abnormal ALP values are not diagnostic, but may indicate an underlying cause.

High values

Abnormally high ALP values may be due to:

Low values

Abnormally low ALP values may be due to:

Other blood tests

An ALP test is usually followed by a test for bilirubin , aspartate aminotransferase (AST), and alanine aminotransferase (ALT) . These tests measure the amount of substances that enter the bloodstream when the liver is damaged. If the bilirubin, ALT, and AST values are normal, this indicates that the liver is not affected and allows the doctor to look elsewhere for the cause.

There is also a bone-specific blood test called bone alkaline phosphatase (BAP), which determines the type of alkaline phosphatase released into the blood from the bones. This can confirm if the condition of the bones causes an increase in alkaline phosphatase compared to the liver .

To identify the cause, your doctor may also order blood tests to detect hormonal imbalances (such as thyroid or parathyroid disease), generalized inflammation and increased white blood cell count (signs of infection), kidney enzyme abnormalities, and various markers . tumorous . in the blood, indicating the presence of cancer.

Based on the results of these blood tests, the healthcare provider may expand the study and order the appropriate tests and procedures (including imaging studies and biopsies ) to definitively diagnose the cause.

Get the word of drug information

Alkaline phosphatase is an important marker for diseases and conditions that affect the liver, bones, and other parts of the body. For an ALP test to be accurate, you need to make sure you follow fasting guidelines and inform your doctor of any medications you are taking, whether they are prescription, over-the-counter, herbal, dietary, or recreational medications. …

Frequently asked questions

  • An alkaline phosphatase (ALP) test shows how much ALP is in the blood. It is used in conjunction with other blood tests to diagnose potential diseases or conditions.

  • The levels of alkaline phosphatase (ALP) that are considered normal vary with age and the stage of pregnancy. In adults, an ALP level of 33 to 96 enzyme units per liter (U / L) is considered normal. For children, this range is less than 350 U / L. The first trimester of pregnancy is 17 to 88 U / L, the second trimester is 25 to 126 U / L, and the third trimester is 38 to 229 U / L. L.

  • If your blood test results show high levels of alkaline phosphatase (ALP), this could indicate liver damage or bone disease. If liver damage is suspected, high ALP levels may indicate cirrhosis (scarring of the liver), hepatitis (inflammation of the liver), bile duct obstruction, or mononucleosis ('kissing disease').

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