Present in several tissues, alkaline phosphatase is an important enzyme for the liver's activity, because it has a higher concentration in the cells of the bile ducts, which transport bile from the liver to the intestine. In the case of bones, on the other hand, it is produced by the cells responsible for the formation and maintenance of bone health.

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What the exam is for

The alkaline phosphatase test, named after the enzyme, is useful for discovering liver and bone dysfunction and disease. The procedure is simple, done in a laboratory and taken through a blood sample. It is ordered in conjunction with several other tests when there are warning symptoms - dark urine, abdominal pain, itching in the body, light stools, bone pain and deformities,for example.

The alkaline phosphatase is also requested for the purpose of a check up The following are the alkaline phosphatase levels by age group*.

• <2 years: 85 - 235 U/L;
• 2 - 8 years: 65 - 210 U/L;
• 9 - 15 years: 60 - 300 U/L;
• 16 - 21 years: 30 - 200 U/L;
• Above 21 years of age: 46 to 120 U/L (acceptable limit: 130 U/L).

*These values may vary according to the laboratory that will do the exam.

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High versus low alkaline phosphatase

When there is an abnormality in the liver, its increase can be related to liver damage, such as hepatitis, cirrhosis, cholestasis, blockage of the bile ducts caused by gallstones, AIDS, and hyperthyroidism.

For bones, their elevated levels may be associated with a recent fracture (which triggers increased production of bone cells to heal the injured area), tumors, Paget's disease (a condition of abnormal growth of some bones), and rickets. Other causes:

• High-fat diet, because it overloads the liver function;
• Renal failure;
• Pregnancy: an increase is common during this phase because of the development of the baby and the presence of alkaline phosphatase in the placenta;
• Bone growth.

When the situation is the opposite, with alkaline phosphatase levels below normal, it can be a sign of malnutrition or anemia, diarrhea, magnesium deficit, hypothyroidism, and even hormone replacement or use of birth control pills. In addition, another problem linked to low indicators is hypophosphatasia, a disease that causes bone deformities and fractures.

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Source: Marcela Araújo, nutritionist at Care Club unity Ipanema (RJ); author of the book "Phytotherapy Applied to Nutrition post-graduated in Functional Sports Nutrition by VP Functional Nutrition Center; updated in Lifestyle Medicine by Harvard Medical School; updated in Obesity Medicine by Harvard Medical School. CRN 418101302.