Alkaline phosphatase in serum
Alkaline phosphatase is widely distributed in human tissues, especially in the intestinal mucosa, osteoblasts, the walls of the bile ducts of the liver, placenta and lactating mammary gland. It catalyses the
for the cleavage of phosphoric acid from its organic compounds;its name is due to the fact that the optimal pH of this enzyme is 8.6-10.1.The enzyme is located on the cell membrane and takes part in the transport of phosphorus. The reference values of alkaline phosphatase activity are presented in Table. For diagnostic purposes, the activity of bone and liver forms of alkaline phosphatase is most often performed.
Table Reference values of serum alkaline phosphatase activity( reaction with phenylphosphate)
Table Reference values of serum alkaline phosphatase activity( reaction with phenylphosphate)
Bone alkaline phosphatase produces osteoblasts - large single-nucleated cells lying on the surface of bone matrix in places of intensive bone formation. Apparently, due to the extracellular location of the enzyme in the process of calcification, it is possible to trace the direct relationship between bone disease and enzyme activity in serum. In children, alkaline phosphatase is increased until puberty. Increased activity of alkaline phosphatase accompanies rickets of any etiology, Paget's disease, bone changes associated with hyperparathyroidism. The enzyme activity increases rapidly with osteogenic sarcoma, metastases of cancer in the bone, myeloma, and lymphogranulomatosis with bone damage.
The activity of the hepatic form of phosphatase is most often increased due to damage or destruction of hepatocytes( hepatic cell mechanism) or biliary transport disorders( cholestatic mechanism).The liver-cell mechanism of increasing the activity of alkaline phosphatase plays a leading role in viral and autoimmune hepatitis, toxic and medicinal liver damage. The outflow of bile is disturbed due to extrahepatic obstruction of the bile ducts( for example, by a stone or with the development of postoperative stricture), narrowing of the intrahepatic ducts( for example, with the primary sclerosing cholangitis), damage to the bile ducts( for example, in primary biliary cirrhosis) orviolations of the transport of bile at the level of small bile ducts( with the use of a number of drugs, for example, chlorpromazine).In some cases, the activity of alkaline phosphatase increases due to the simultaneous action of both mechanisms of damage. Increase in activity of alkaline phosphatase in liver damage occurs due to its release from hepatocytes. The activity of alkaline phosphatase in viral hepatitis, in contrast to aminotransferases, remains normal or increases slightly. An increase in the activity of alkaline phosphatase is found in icteric patients with cirrhosis of the
liver( in a third of cases).Approximately half of patients with infectious mononucleosis in the first week of the disease also notice an increase in activity of alkaline phosphatase. A significant increase in the activity of alkaline phosphatase is observed with cholestasis. The extrahepatic occlusion of the bile ducts is accompanied by a sharp increase in the activity of the enzyme. An increase in the activity of alkaline phosphatase is observed in 90% of patients with primary liver cancer and with metastases to the liver. Sharply increases its activity in alcohol poisoning against the background of alcoholism. It can increase when taking drugs that have a hepatotoxic effect( tetracycline, paracetamol, mercaptopurine, salicylates, etc.).Cholestatic jaundice and, accordingly, increased activity of alkaline phosphatase are possible in women taking oral contraceptives containing estrogens and progesterone. According to different authors, only about 65% of hospitalized patients have high activity of alkaline phosphatase due to liver diseases.
Very high activity of the enzyme is observed in women with pre-eclampsia, which is associated with placental lesions. Reduced activity of alkaline phosphatase in pregnant women may indicate a lack of development of the placenta.
In addition to the above reasons, the increase in activity of alkaline phosphatase is revealed in the following diseases and conditions: increased metabolism in bone tissue( with healing of fractures), primary and secondary hyperparathyroidism, osteomalacia, renal rickets, cytomegalovirus infection( CMV infection) in children, sepsis, ulcerative colitis, regional ileitis, intestinal bacterial infections, thyrotoxicosis. This is due to the fact that alkaline phosphatase is produced not only in the liver, but also in other organs - bones, intestines.
Values of activity of alkaline phosphatase( thresholds for making clinical decisions) in establishing a clinical diagnosis of liver damage are presented in Fig.[Menshikov VV, 2002].A number of values are multipliers multiplied by the value of the upper reference limit for alkaline phosphatase.
A decrease in enzyme activity is noted in hypothyroidism, scurvy, severe anemia, kwashiorkor, hypophosphatemia.