Alkaline phosphatase is a marker enzyme

In practice, clinicians often encounter an unexpected increase in alkaline phosphatase activity. Thanks to the use of multi-profile test kits for biochemical research, it became possible to control the activity of this enzyme. By the level of activity of this enzyme can detect diseases of the hepatobiliary system and bone tissue.

Alkaline phosphatase is an enzyme that belongs to the hydrolase class, which removes the phosphate group from different biopolymers (proteins, nucleic acids, alkaloids). The greatest activity of the enzyme is observed in an alkaline medium. The enzyme is in cells in the plasma-bound state, and therefore refers to membrane-bound enzymes. Alkaline phosphatase (APF) consists of different isoenzymes that are located in the epithelium of the bile ducts, plasma membranes of hepatocytes and neurons, bones, intestines, placenta, kidneys.

The activity of isoenzymes can be determined by electrophoresis. However, the isoenzymes of alkaline phosphatase do not have a clear organ specificity, and the electrophoretic technique is very complicated. Therefore, to simplify the research use a technique that is based on the different sensitivity of isoenzymes to heat. Intestinal alkaline phosphatase refers to a thermostable fraction, and isoenzymes from the liver and bone tissue are thermolabile. The most sensitive to heat is bone phosphatase.

Serum alkaline phosphatase is a mixture of bone and liver isoenzymes. The intake of an enzyme from different tissues into the blood depends on the physiological state and age of the organism (pregnancy, childbirth, lactation intensity). High activity of AP in the blood of young people is due to the intensive functioning of osteoblasts in bone tissue, which are caused by the processes of active growth of the body. During this period, the activity of the enzyme in the blood increases due to the bone isoenzyme. In the second half of pregnancy and during childbirth, the active increase and destruction of the placenta causes an increase in the concentration of the placental isoenzyme.

An increase in the concentration of alkaline phosphatase in the blood is most often recorded with pathology of the liver and bone tissue. The defeat of the liver parenchyma causes a slight increase in the activity of the enzyme in the serum, since alkaline phosphatase is bound to the cell membranes. In clinical hepatology, the hepatic isoenzyme is indicative for the diagnosis of cholestasis. This is due to increased synthesis of alkaline phosphatase cells in the bile ducts and a violation of the isolation of the enzyme in bile. Especially high is hyperfermentemia in the development of the pathological process and stasis of bile in the hepatic bile ducts. Then the enzymatic activity of AP in the serum increases tens of times. If the intrahepatic bile ducts are damaged, the activity of the enzyme in the blood increases only by 2-3 times. The norms of alkaline phosphatase for adults up to 31 years are 39.0-92.0 IU / l, after 31 years - 39.0-117.0 IU / l. Alkaline phosphatase is normal in children under 10 years - 106.0-213.0 IU / L, up to 3 years - 71.0-213.0 IU / L, and for newborns - 35.0-106.0 IU / L.

In the pathology of bone tissue, when there is increased activity of osteoclasts, during the development of rickets, osteodystrophy, hyperparathyroidism in the blood, the activity of bone alkaline phosphatase increases. At the same time, the activity of the common AF in the blood increases 3-10 times. For early diagnosis of rickets and osteodystrophy, the increase in phosphatase activity in the synovial fluid is specific . An increase in the activity of AF in the cerebrospinal fluid is a sign of damage to neuronal membranes, where it is localized.