What is the leukocyte count in a 1:20 diluted EDTA-anticoagulated specimen with 132 leukocytes counted in the four corner squares of a hemacytometer?

Calculation of Leukocyte Count in a Hemacytometer

The leukocyte count for the given specimen is 6.6 x 10³/μL (answer B).

Calculation Method

To determine the leukocyte count from a hemacytometer count, we need to apply the appropriate formula based on the dilution factor and counting area used:

1. Given information:

   • Dilution factor: 1:20
   • Number of leukocytes counted: 132
   • Counting area: Four corner squares of the hemacytometer

2. The formula for calculating leukocyte count is:

   • Leukocyte count = (Number of cells counted × Dilution factor × Depth factor) ÷ Volume counted

3. For a standard hemacytometer:

   • Each corner square has a volume of 0.1 mm³
   • Four corner squares = 0.4 mm³
   • Depth factor = 10 (to convert mm³ to μL)

4. Calculation:

   • Leukocyte count = (132 × 20 × 10) ÷ 4
   • Leukocyte count = 26,400 ÷ 4
   • Leukocyte count = 6,600 cells/μL or 6.6 × 10³/μL

Hemacytometer Counting Principles

The hemacytometer is a specialized counting chamber used for determining cell concentrations in fluid samples. When performing manual leukocyte counts:

• The sample must be properly diluted to ensure accurate counting
• The dilution factor (1:20 in this case) must be incorporated into the calculation
• Only cells within the designated counting areas should be counted
• The four corner squares are standard counting areas for leukocytes
• Each corner square has a volume of 0.1 mm³, so four squares equal 0.4 mm³

Clinical Significance of Leukocyte Counts

Normal leukocyte count ranges typically fall between 4.5-11.0 × 10³/μL, though some research suggests a narrower range of 3.11-8.83 × 10³/μL based on normal C-reactive protein levels. The calculated value of 6.6 × 10³/μL falls within the normal reference range.

Accurate leukocyte counts are essential for:

• Diagnosing infections and inflammatory conditions
• Monitoring disease progression
• Evaluating response to therapy
• Assessing immune system function

Common Pitfalls in Manual Leukocyte Counting

• Improper sample dilution
• Uneven cell distribution in the counting chamber
• Counting cells that touch boundary lines incorrectly
• Mathematical errors when applying the formula
• Failure to account for the correct counting area volume

Manual leukocyte counts require precision and attention to detail to ensure accurate results that can be used for clinical decision-making.