What is the most reliable method to obtain accurate White Blood Cell (WBC) count results when only 2 WBCs are counted in a 1:10 dilution in all 9 squares on a hemacytometer?

Obtaining Reliable WBC Count Results with Low Cell Counts

When only 2 WBCs are counted in a 1:10 dilution across all 9 squares of a hemacytometer, the most reliable results would be obtained by performing an automated cell count (option B).

Analysis of the Scenario

When analyzing the given scenario, we need to consider the statistical reliability of the count:

• Only 2 WBCs were counted in all 9 squares
• The sample was diluted 1:10
• This represents an extremely low cell count

Statistical Considerations

The analytic variability (CV) in determining WBC counts varies significantly between methods:

• Manual hemacytometer counts: 9.3%-17.6% CV 1
• Automated leukocyte counters: 2.2%-7.7% CV 1

With only 2 cells counted across all 9 squares, the statistical reliability is extremely poor. The coefficient of variation for manual counting is inversely related to the number of cells counted, with particularly high variability at low cell counts.

Evaluation of Options

Option A: Recounting on an undiluted sample

• Would increase the number of cells counted
• However, manual hemacytometry remains subject to high variability (9.3%-17.6%) 1
• User-to-user variation and subjective decisions remain problematic 2

Option B: Automated cell count

• Significantly lower variability (2.2%-7.7%) 1
• Higher precision, especially with low cell counts 3
• Eliminates user bias and subjective decision-making 2
• Automated counters have shown coefficients of variation of 2.9-20% compared to 10.7-27.9% for manual counts 3

Option C: Counting an additional 9 square millimeters

• Would increase the sample size
• However, still subject to the inherent limitations of manual counting
• Sources of error in hemocytometry include uneven cell distribution, subjective decisions, and user-to-user variation 2

Option D: Reporting the WBC count as 22/cumm

• This appears to be a calculation based on the current count
• With only 2 cells counted, the statistical reliability would be extremely poor
• CDC guidelines recommend counting at least 2,500 gated lymphocytes to ensure accuracy 1

Best Practice Recommendation

For samples with very low cell counts, automated methods provide significantly better precision and reliability. The CDC guidelines acknowledge that automated methods have substantially lower variability than manual counting 1.

Key advantages of automated counting:

• Higher precision with coefficients of variation 3-10 times better than manual methods 3
• Elimination of subjective errors and user bias 2
• Better reproducibility and repeatability 4
• Particularly advantageous for low cellularity samples where statistical reliability is most challenging 3

Common Pitfalls to Avoid

1. Relying on manual counts with very low cell numbers: With only 2 cells counted, the statistical reliability is extremely poor regardless of technique.

2. Failing to recognize when a different methodology is needed: When cell counts are extremely low, switching to a more sensitive and precise method is appropriate.

3. Reporting results with insufficient statistical reliability: Results based on counts of only 2 cells have extremely wide confidence intervals and should not be reported without verification by more reliable methods.

In conclusion, when faced with a sample where only 2 WBCs were counted in a 1:10 dilution across all 9 squares of a hemacytometer, an automated cell count would provide the most reliable results due to its superior precision and reproducibility, especially for samples with low cellularity.