wbc differential count test principle, procedure

WBC differential count test gives relative numbers of different types of WBC (leucocytes) in the well-spread and perfect blood smear.

Even the distribution of white blood cells depends on meticulous techniques of blood film preparation. while the correct identity of white blood cells depends upon the quality of the stain.

Note: If the edge of the spreader is ROUGH, then many WBC especially neutrophils, and monocyte predominate at the margins and the tail.While lymphocytes predominate in the middle of the blood film.

WBC differential count Procedure

Following is the procedure of differential counting white blood cells.

  1. Prepare perfect blood smear.
  2.  Chose the middle portion of fim, where cells are evenly spread when seen under a low-resolution compound light microscope. Now place a drop of CEDARWOOD OIL, and move the oil emersion objective in place.
  3. Start count and identify each type of cell from TAIL of film and move toward the head in the linear strip.
  4. When a single strip is completed, adjust the lens to another position vertically upward or downward. The counting Counting of cells is started again but in the reverse direction. 
  5. This WBC counting procedure is continued until 100 cell count.
  6. If the cells number are high, count 250 to 300 cells in order to get an accurate idea of the relative number of WBC.
  7. IF there is one BASOPHIL in 100 cells, then another hundred cells should be counted to estimate their correct percentage.
  8. If there are nucleated red blood cells, these are not included in the white blood cells, instead, these are counted separately and reported as NUCLEATED RED CELL in 100 cells.
  9. DLC (Differential leucocyte count) is reported as a percentage.

Following cells are counted in WBC differential count test.

  • Neutrophil
  • Eosinophils
  • Basophil
  • Lymphocyte
  • Monocyte

Note: Various maturation stages of WBC like blast, metamyelocytes, promyelocyte, and band forms included.

Blood cell count and differential normal range

DLC consist of 
  • Neutrophils
  • lymphocyte
  • Eosinophils
  • Basophils
  • Monocyte
white blood cell differential test range chart is 
wbc differential normal range

What are the common problems in WBC differential count?

We can face the following problems in the white blood cell differential count. 

  • If there is more than expected WBC in blood film, then there is more chance of cell accumulation in the middle portion of blood film. This problem occurs due to improper blood film preparation technique of faulty spreader.
  • Cell identifying problem. It occurs due to
  • Poor staining
  • Cell denaturation
  • Cell naturation: It occurs in the following conditions.
  1. Smear preparation delay (5 hours)
  2. Improper anticoagulantant
  3. Severe Septicemia
  • Vaculatio of Monocyte
  • Activation of lymphocyte

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