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Diagnostic Tests 2023

Alkaline Phosphatase: what é and why está high or low

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Alkaline Phosphatase: what é and why está high or low
Alkaline Phosphatase: what é and why está high or low

Alkaline phosphatase is an enzyme that is present in various tissues of the body, being in greater quantity in the cells of the bile ducts, which are the channels that carry bile from the liver to the intestine, and in the bones, being produced by the cells involved in its formation and maintenance.

The alkaline phosphatase test is generally used to investigate liver or bone diseases, when signs and symptoms such as abdominal pain, dark urine, jaundice or bone deformities and pain are present, for example. It can also be performed as a routine exam, along with other exams, to assess liver he alth.

Although in lower amounts, alkaline phosphatase is also present in the placenta, kidneys and intestine, and may therefore be elevated in pregnancy or in cases of renal failure.


What is it for

The alkaline phosphatase test is used to investigate liver or bone disorders and its result can identify:

1. High alkaline phosphatase

Alkaline phosphatase may be elevated when there are liver problems such as:

  • Biliary flow obstruction, caused by gallstones or cancer, which block the channels that carry bile to the intestine;
  • Hepatitis, which is an inflammation of the liver that can be caused by bacteria, viruses or toxic products;

  • Cirrhosis, which is a disease that leads to the destruction of the liver;
  • Consumption of fatty foods;
  • Kidney failure.

In addition, this enzyme can be very high in situations where there is an increase in bone formation activity, such as in some types of bone cancer or in people with Paget's disease, which is a disease that is characterized by the abnormal growth of certain parts of the bones. Learn more about Paget's disease.

Slight changes may also occur during periods of fracture healing, pregnancy, AIDS, intestinal infections, hyperthyroidism, Hodgkin's lymphoma, or even after a high-fat meal.

2. Low alkaline phosphatase

Alkaline phosphatase levels are rarely low, however this enzyme may be decreased in the following situations:

  • Hypophosphatasia, which is a genetic disease that causes deformities and fractures in the bones;
  • Malnutrition;
  • Magnesium deficiency;

  • Hypothyroidism;
  • Severe diarrhea;
  • Severe anemia.

Furthermore, some drugs such as the birth control pill and hormone replacement therapy drugs used in menopause can also cause a slight decrease in alkaline phosphatase levels.

When to take the exam

Alkaline phosphatase testing should be performed when signs and symptoms of liver disorders are present, such as enlarged abdomen, pain on the right side of the abdomen, jaundice, dark urine, pale stools, and generalized itching.

In addition, this exam is also indicated for people who have signs and symptoms at the bone level such as generalized bone pain, bone deformities or who have suffered fractures.

How the exam is done

The test can be performed in a laboratory, where a he althcare professional takes about 5 ml of a blood sample from a vein in the arm, which is placed in a closed container for analysis.

Reference values

Alkaline phosphatase test reference values vary with age due to growth:

Children and teenagers:

  • < 2 years: 85 - 235 U/L
  • 2 to 8 years: 65 - 210 U/L
  • 9 to 15 years: 60 - 300 U/L
  • 16 to 21 years: 30 - 200 U/L


46 to 120 U/L

In pregnancy, alkaline phosphatase blood values may be slightly altered, due to the growth of the baby and because this enzyme is also present in the placenta.

Along with this exam, other enzymes found in the liver such as alanine aminotransferase, aspartate aminotransferase, gamma glutamyl transpeptidase and bilirubins, imaging tests or even a liver biopsy can also be performed. See how these exams are performed.

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