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