Alkaline phosphatase (ALP) can be found in non-segmented and segmented neutrophilic granulocytes of the circulating blood and the bone marrow.
Clinical significance of this enzyme is that its activity is absent or decreased in chronic myelogenous leukemia, which is evident often before clinical manifestation of the disease, and in paroxysmal nocturnal hemoglobinuria.
Increased ALP activity is found in polycythemia vera, thrombocytemia, acute lymphatic leukemia, and in pernicious anemia during reticulocytic crisis.
The substrate, naphtol AS-BI phosphate, is hydrolyzed to phosphate and an aryl naphtholamide by alkaline phosphatase. Aryl naphtholamide is coupled to a diazonium salt, such as fast red violet pigment, forming an insoluble dye, which are readily visualized in neutrophilic leukocytes that contain alkaline phosphatase activity.
The results are expressed as the phosphate index of five after counting 100 neutrophils (90 segmented and 10 non-segmented). According to the intensity, degree of strength of positive reaction they are categorized in classes.
Scoring Criteria for Rating Neutrophils Stained for Alkaline Phosphatase Activity
Intensity step
Intensity of reaction
Normal values
Intensity of staining
0
Negative
80% neutrophilic granulocytes
No reaction.
1
Little positive
18% neutrophilic granulocytes
Single to few granules.
2
Little positive
18% neutrophilic granulocytes
Many granules localized.
3
Grand positive
1% neutrophilic granulocytes
Granules diffuse distributed.
4
Grand positive
1% neutrophilic granulocytes
Cell complete with granules overcast.
5
Grand positive
1% neutrophilic granulocytes
Maximum number of granules, nucleus frequently no longer visible.
