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Alkaline Phosphatase and Isoenzymes

Alkaline Phosphatase and Isoenzymes

Synonyms - Specimen - Reference Value - Method - Description - Indications - Interpretation 

Synonyms : ALK Phos , ALP and fractionation , heat- stable ALP . 
Specimen : Serum or plasma 
Reference Value : 41 - 133 IU/L
Method : Spectrophotometry ( for total alkaline phosphatase , inhibition / electrophoresis for fractionation ) .

Description 

ALP is non organ specific enzyme found in the liver , in Kupffer cells lining the biliary tract , and in bones , intestines , and in placenta . Additional soures of ALP include the proximal tubules of the kidneys , pulmonary alveolar cells , germ cells , vascular bed , lactating mammary glands , and granulocytes of circulating blood . ALP is referred to as alkaline because it functions optimally at a PH of 9.0 . This is most usefule for determined the presence of liver and bones diseases . Isoelectric focusing  can identify 12 isoenzymes  of ALP . Four main ALP isoenzymes, however , are of clinical significance : ALP1 of liver origin , ALP2 of bone origin , ALP3 of intestinal origin , ALP4 of placenta origin ( third trimester ) . 
ALP levels vary by age and gender .Values in children are higher than in adults because of the level of bone growth and development . An immunoassay method is available for measuring bone - specific 
ALP as an indicator of increased bone turnover . The enzyme is associated with microsomal membranes .ALP is anchored to cell membranes by glycophosphatidylinositol  (GPI ) proteins .
Cleavage of these proteins by bile acids , phospholipase D and proteases releases AP from memberanes resulting in increased AP levels in serum / plasma . 

Indications 

- Elevated various disorders associated with elevated ALP levels , such as biliary obstruction , hepatobiliary disease . and bone disease . 

- Differentiate obstructive hepatobiliary tract disorders from hepato cellular disease , greater elevations of ALP are seen in the former ( it is one of Cholestatic enzymes ) 

- Determine effects of renal disease on bone metabolism 
- Determine bone growth or destruction in children with abnormal growth patterns . 

Interpretation 

Increased in 

Liver disease

- Biliary atresia 
- Biliary obstruction : Extra-hepatic cholestasis ( bile duct obstruction ) : This causes very dramatic increases in AP . Increases in AP may occur before development of icterus  . 
- Chronic active hepatitis ( hepatocellular   swelling and intra hepatic cholestasis occur 
- Cirrhosis 
- Diabetes mellitus ( diabetic hepatic lipidosis )
- Extrahepatic duct obstruction ( Pancreatitis ( acute or chronic ) may result in increased AP levels from swelling and / or fibrosis around the bile duct ). 
- Granulomatous or infiltrative liver diseases 
- Viral hepatitis 

Bone disease 

- Healing fructures 
- Metabolic bone diseases ( rickets , osteomalacia ) 
- metaststic tumors in bone 
- Osteogenic sarcoma 
- Ostoporosis 

Other conditions 

- Advanced pregnancy 
- Cancer of pancreas 
- Chronic real failure 
- Congestive heart failure 
- Growing children 
- Hyperparathyroidism ( Primary or secondary to chronic renal disease ) 
-Ulcerative colitis 

Decreased in 

- Anemia ( sever ) 
- Hypophosphatasia 
- Nutritional deficiency of zinc or magnesium 




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