Which statement correctly describes estimating WBC count from a smear?

Which statement correctly describes estimating WBC count from a smear?

• A. Count the number of WBCs per field in ten monolayer fields at 40x; determine the average by dividing the sum of counts by ten; multiply the average by 2000.
• B. Count the number of WBCs per field in ten monolayer fields at 40x.
• C. Count the number of WBCs per field in five monolayer fields at 40x, then multiply the average by 2000.
• D. Count WBCs in a single field and multiply by 2000.

Answer: (B)

Estimating WBC count from a smear relies on sampling several fields at high magnification to get a representative count. Using the 40x objective to view monolayer areas and counting white cells across multiple fields reduces the sampling error that comes from uneven distribution of cells on the smear. The counts from these fields are then averaged and scaled by a conversion factor (commonly 2000) to estimate the WBC count per microliter. Counting WBCs across ten monolayer fields at 40x provides the necessary adequate sample size to form a reliable average, which is why this approach is preferred. The other options either under-sample (fewer fields or a single field) or omit the essential averaging and scaling steps, making the estimate less accurate.

Estimating WBC count from a smear relies on sampling several fields at high magnification to get a representative count. Using the 40x objective to view monolayer areas and counting white cells across multiple fields reduces the sampling error that comes from uneven distribution of cells on the smear. The counts from these fields are then averaged and scaled by a conversion factor (commonly 2000) to estimate the WBC count per microliter. Counting WBCs across ten monolayer fields at 40x provides the necessary adequate sample size to form a reliable average, which is why this approach is preferred. The other options either under-sample (fewer fields or a single field) or omit the essential averaging and scaling steps, making the estimate less accurate.