Alkaline phosphatase (ALP) is an exoenzyme of osteoblasts, and its expression activity is an obvious feature of osteoblast differentiation. The main physiological function of alkaline phosphatase in the body is to hydrolyze phosphate esters during the osteogenesis process, providing necessary phosphoric acid for the deposition of hydroxyapatite, and at the same time hydrolyzing pyrophosphate to relieve its inhibitory effect on the formation of bone salts. Conducive to osteogenesis.
Clinical measurement of ALP is mainly used for the diagnosis and differential diagnosis of bone, hepatobiliary system diseases, especially the differential diagnosis of jaundice. For unexplained high ALP serum levels, isoenzymes can be measured to help determine the organ source.
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Physiological increase
In children during the physiological bone development period, alkaline phosphatase activity can be 1 to 2 times higher than that of normal people. It can increase in adolescents during their growing years, as well as in pregnant women and after eating foods high in fat content.
Clinical significance
Pathological elevation of total serum ALP is 60% likely to be caused by liver and biliary tract diseases. ALP is a sensitive indicator of cholestatic diseases.
01 Extrahepatic bile duct obstruction
ALP is elevated in the early stage. Common clinical symptoms include: 1. Malignant obstruction such as pancreatic head cancer and cholangiocarcinoma. ALP was significantly increased. 2. The degree of increase in benign obstruction caused by bile duct stones and inflammation is lower than that of malignant obstruction. 3. ALP may increase in cholecystitis, cholelithiasis, and sclerosing cholangitis.
02 Intrahepatic cholestasis
In cholestatic hepatitis and intrahepatic cholestasis caused by drugs and ethanol, the degree of ALP increase is often lower than that of extrahepatic malignant biliary obstruction.
03 Intrahepatic space-occupying lesions
The increase in ALP in primary hepatocellular carcinoma is more obvious than the increase in transaminases; ALP with large molecular weight may appear in metastatic hepatocellular carcinoma.
04 Viral hepatitis, cirrhosis and other parenchymal liver lesions
If there is no obstruction of the bile duct system and cholestasis, ALP is usually normal or slightly elevated. If bile duct stasis and cholestasis occur at the same time, jaundice will be accompanied by a significant increase in ALP.
The meaning of reduction
Reduced ALP activity in children will affect bone development and even stop bone development, leading to clinical cretinism, achondroplasia and cachexia;
Reduced ALP activity is more common in older women, which may be related to the reduced estrogen secretion in older women after menopause, which affects bone resorption, and osteoporosis reduces serum ALP activity.
Severe chronic nephritis, thyroid insufficiency in children, and anemia will also be reduced.
In summary
Reduced serum ALP activity is mainly seen in severe chronic nephritis accompanied by renal failure, malnutrition and thyroid insufficiency, magnesium deficiency, celiac disease, severe anemia, etc. There is also a hereditary low-A Cabot LP disease, in which infants are deficient in serum ALP and lack this enzyme in osteoblasts, causing severe mineral deficiency in the bones and prone to fractures.
