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 %

Buffered substrate PH 10
0.5 ml
0.5 ml
0.5 ml
D / W
1.55 ml
1.55 ml
1.55 ml
Mix well and incubate at 37ᵒ for 15 min
Phenol STD
Mix well and incubate at 37ᵒ for 15 min
Colored reagent
1 ml
1 ml
1 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
  • Malnutrition