Alkaline Phosphatase: What It Is and Why It's High or Low

Content:

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 their training and maintenance.

The alkaline phosphatase test is usually used to investigate liver or bone diseases, when signs and symptoms are present, such as pain in the abdomen, dark urine, jaundice or bone deformities and pain, for example. It can also be performed as a routine test, along with other tests, to assess liver health.

Alkaline phosphatase, although in lower amounts, 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:

  • Obstruction of bile flow, 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;

  • Renal insufficiency.

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 characterized by the abnormal growth of certain bone parts. Learn more about Paget's disease.

Mild changes can 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.

In addition, 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

The alkaline phosphatase test should be done when signs and symptoms of liver disorders are present, such as an enlarged abdomen, pain in 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 healthcare 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 old: 30 - 200 U/L

Adults:

  • 46 to 120 U/L 

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

Along with this test, 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 tests are done .