What does alkaline phosphatase do

All NetDoktor content is checked by medical journalists.

The alkaline phosphatase (AP, ALP, bone-specific ostasis) is an enzyme that is involved in many metabolic processes in the body. There are different groups of alkaline phosphatases. It is located in the bone cells and liver tissue, among other things. With an increased metabolism, for example in the bones, the bone-specific AP can be increasingly detected in the blood. Read everything you need to know about alkaline phosphatase here.

What is alkaline phosphatase?

Alkaline phosphatase (AP) is a metabolic enzyme that occurs in various organs and structures in the body - such as the skeleton or the liver. If, for example, more bone is built up (as in growth or after a bone fracture), it can also be increasingly detected in the blood.

There are different types of alkaline phosphatase. These are each named after the tissue in which they predominantly occur.

Alkaline phosphatase is mainly found in the bone skeleton, in liver tissue and in the cells of the bile ducts. If the concentration of alkaline phosphatase in the blood is increased, this can indicate processes or diseases in these structures.

When is alkaline phosphatase determined?

The concentration of alkaline phosphatase in the blood is mainly determined if the doctor suspects bone tumors or bone metastases, or if there are symptoms of liver disease. The concentration of the alkaline phosphatases of all subgroups is measured.

Alkaline phosphatase: reference values

The concentration of alkaline phosphatase in the blood is not expressed in its absolute dose, but in enzyme activity units (units, U) per liter of substrate. The following standard values ​​apply (measurement at 37 ° C):

When is alkaline phosphatase low?

The alkaline phosphatase level is very rarely too low. This occurs, for example, with pronounced hypothyroidism or anemia. The rare hereditary disease Wilson's disease manifests itself in a disturbed copper metabolism. Here, too, the alkaline phosphatase can be too low. Achondroplasia and hypophosphatasia, two hereditary diseases, are also associated with decreased levels of alkaline phosphatase.

When is alkaline phosphatase increased?

If bone, liver or kidney disease is suspected, the doctor will also determine alkaline phosphatase in addition to other blood values. The concentration in the blood is increased in the following diseases:

  • Liver diseases such as tumors, hepatitis, bile duct congestion, bile duct inflammation
  • Bone diseases such as bone tumors, Paget's disease, rickets (vitamin D deficiency)
  • certain types of kidney failure (kidney failure)
  • Acromegaly (excess growth hormone) and Cushing's syndrome (excess cortisol)
  • Overactive parathyroid glands

During pregnancy and during child growth, alkaline phosphatase is also increasingly detectable in the blood. In these cases, however, it is a question of a non-pathologically increased concentration.

Taking various medications such as allopurinol (gout medication), anti-epileptic drugs or the contraceptive pill can also increase the AP value.

What to do if the AP level has changed?

If the alkaline phosphatase can be detected in the blood, this does not necessarily mean a disease. Therefore, if the values ​​change, further examinations must always be carried out in order to clarify the cause. The doctor will monitor the course of the alkaline phosphatase-Check the concentration if the values ​​change.

Author & source information