Calculation of Total WBC Count on a Neubauer Hemacytometer
The patient's total WBC count is 9000/mm³ (option C).
Understanding the Calculation
When performing a manual WBC count using a Neubauer hemacytometer, the following formula applies:
WBC count/mm³ = (Number of cells counted × Dilution factor) ÷ (Area counted in mm² × Depth of chamber)
Let's break down the components of this calculation:
- Number of cells counted: 360 cells
- Dilution factor: 1:10 (which equals 10)
- Area counted: 4 square millimeters
- Depth of chamber: 0.1 mm (standard for Neubauer hemacytometer)
Step-by-Step Calculation
- Apply the formula: WBC count/mm³ = (360 × 10) ÷ (4 × 0.1) WBC count/mm³ = 3600 ÷ 0.4 WBC count/mm³ = 9000
Clinical Relevance
The calculated WBC count of 9000/mm³ falls within the normal reference range for adults (typically 4,000-11,000/mm³) 1. This is important because:
- WBC counts are crucial diagnostic indicators in various clinical scenarios
- Accurate manual counting techniques remain important for verification of automated results
- The Neubauer hemacytometer is a standard tool for cell counting in laboratory medicine
Common Pitfalls in Manual WBC Counts
- Failing to account for the dilution factor (which would result in a count of 900/mm³)
- Miscalculating the area counted (using only one square millimeter would yield 36,000/mm³)
- Not considering the depth of the chamber (standard depth is 0.1 mm)
- Inadequate mixing of the sample before loading the hemacytometer
- Poor technique in filling the chamber, leading to uneven cell distribution
Verification
To verify the accuracy of manual counts, laboratories should:
- Perform duplicate counts when possible
- Compare with automated analyzer results when available
- Ensure proper maintenance and calibration of the hemacytometer
- Follow standardized procedures for sample preparation and counting
The correct answer is C: 9000/mm³, which represents the patient's total WBC count based on the provided data.