Estimation of alkaline phosphatase in serum – liver function tests


Estimation of alkaline phosphatase in serum


Phosphatase are enzymes which catalyze the splitting of phosphoric acid from certain mono phosphoric esters such as (glycerophosphates and phenyl phosphates)

Alkaline phosphatase with a maximum activity at about PH 10


Alkaline phosphatase in serum acts on the substrate disodium phenyl phosphate buffered at PH 10 at 37ᵒ to liberate phenol

This phenol condenses with 4- amino antipyrine in the presence of alkaline oxidizing agent potassium ferricyanide to give red colored complex which is measured at 520 nm

Normal range                 

Alkaline phosphatase : 21 – 92 IU / L or 3 – 13 KA units

Note : one IU of ALP activity = 7.13 KA units


Buffered substrate PH 10

Phenol std

Chromogen reagent 4 – amino antipyrine 0.6 % , potassium ferricyanide 2.4 % Procedure

Buffered substrate PH 100.5 ml0.5 ml0.5 ml
D / W1.55 ml1.55 ml1.55 ml
Mix well and incubate at 37ᵒ for 15 min
Phenol STD50µ
Mix well and incubate at 37ᵒ for 15 min
Colored reagent1 ml1 ml1 ml
Mix well and read at 520 nm


ALP activity (IU/L) = Serum ALP levels are increased in:

Liver diseases: enzyme is produced by the hepatocytes canaliculi and hence marked increase is seen in condition of obstruction of bile flow

Extrahepatic biliary obstruction due to : stones in bile duct , cancer of head of pancreas

Intrahepatic biliary obstruction due to : viral / drug induced hepatitis or malignancy

:Bone diseases: when osteoblastic activity in bone formation is take place like in

Rickets : values of ALP more than 100 KA units can be seen

Osteomalacia : less rise than in rickets

Paget’s disease : very high values seen

Others: fanconi’s syndrome, hyperparathyroidism

:Serum ALP levels are decreased in

Severe anemia