Determination of WBC Differential Count by Microscopic Method

A WBC Differential Count, also known as a Differential Leukocyte Count (DLC), measures both the relative proportions and absolute numbers of various types of white blood cells (WBCs) in a blood sample. This test is crucial for providing diagnostic insights by identifying normal and abnormal leukocytes, which are essential components of the immune system. Leukocytes, or white blood cells, circulate in the blood and lymphatic system, where they play pivotal roles in defending against infections, mediating inflammatory responses, managing allergies, and protecting against cancer.

The differential count categorizes WBCs into two main groups: granulocytes (including neutrophils, eosinophils, and basophils) and non-granulocytes (such as lymphocytes and monocytes). It provides detailed information on the percentage of each type. Indications for performing a WBC count include the evaluation of infectious and inflammatory diseases, detection of leukemia and lymphoma, and assessment of bone marrow disorders. The differential count can be performed using two primary methods: the manual (microscopic) method and the automated method.

Detailed Microscopic Method for Performing a WBC Differential Count

Requirement for WBC Differential Count by Microscopic Method

• Stained Peripheral Blood Smear (PBS)
• Microscope with a 100× objective lens
• Cell counter

Step-by-Step Procedure for Accurate Differential Leukocyte Count

It is essential to conduct examinations and counts within the monolayer area of the slide.

1. Scan the slide in a systematic grid pattern to avoid covering the same area twice. Counts can be completed efficiently at 400× magnification; however, if assessing morphology, 1000× magnification should be employed.
2. Count a minimum of 100 WBCs. (If the total WBC count is elevated, count 200 cells to maintain accuracy.)

Calculations for Relative and Absolute WBC Counts

Relative count:

Relative count can be obtained by the following formula:

No. of Cell Type Seen ÷ 100 = Relative Count in %

Absolute count:

Absolute count can be obtained by the following formula:

[Relative count (%) × WBC Count (10³/L)] ÷ 100 = Absolute Count × 10³/μL

Note

• Ensure that the relative counts of each cell type sum to 100.
• The absolute counts of each cell type should total the WBC count.