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Alkaline phosphatase {ALP}
Alkaline phosphatase {ALP}
– ALP are group of enzymes that split off terminal phosphate group from an organic phosphate ester usually around pH 10.0 . It is normally found in bone , leukocytes , placenta , intestinal mucosa , renal tubules , biliary tree and lower conc. in the liver.
– By Isoelecric focusing [IEF] technique ALP separated into 12 isoenzymes they are :- biliary , hepatocytic , hepatic reticuloentestinal , vascular bed , bone pulmonary alveolar cells , neutrophil , fetal intestinal, germ cells placental , activated T lymphocyte , renal and intestinal.
– By the inactivation of ALP isoenzymes by heat we can separate liver , bone and placental isoenzyme at 16 min at 55ċ or 5 min at 65ċ.
– Liver and placental isoenzyme are heat stable but bone isoenzyme are heat labile.
– Prespecimen processing :- The patient should be fast 10-12 hours.
Methodology :-
Kinetic , PNP method.
Clinical significance :-
– Increased total ALP in :- bone metabolism , bone disease , some renal disease , liver disease , pulmonary and renal infarction , panceriatitis.
– Increased bone isoenzyme in :- bone growth , nutritional deficiency of vitamin D, malabsorbtion , bone cancers , lymphoma , osteoporosis , hyperthyroidism.
-Increased biliary ALP in cholestasis.
-Increased intestinal ALP in :- After meal , intestinal diseases.
– Increased liver ALP in :- hepatic congestion , decreased clearance of enzymes , pregnancy , carcinoma , hepatitis and parenchyma cell damage.
-Increased placental ALP in :- During the 3rd trimester of pregnancy.
-Decreased ALP in :- hypothyroidism , scurvy , anemia , nutritional deficiency of Zn or Mg , hypophosphatesemia.
Guiding Reference Value :-
-Total ALP > 20 years M. 25 -175 U/L.
-ALP isoenzymes stability after 16 min incubation at 56 ċ
-Placental 90% stable.
-Liver 50% stable.
-Intestinal 50 % stable
-Bone 10% stable
Limitation :-
-ALP is best indicator for obstructive jaundice and biliary disease if tested together with GGT .
-postmenstrual females has slightly increased ALP .
-hepatotoxic drugs within 12 hours prior to sampling invalidate the test .
-Some drugs cause elevation in ALP levels include :- hepatotoxic drugs , aminoglycosides , captopril , cephalosporins , cyclosporine, interferone , mebendazole , omeprazole , penicillins , phyntoin and sulfonylureas.
-And some reduce the levels such as :- estrogen , zinc and Mg salts and Mn.
Alkaline phosphatase {ALP}
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