In the platelet procedure, how many oil-immersion fields are counted?

• A. 5
• B. 10
• C. 15
• D. 20

Answer: (B)

When estimating platelets on a peripheral smear, the key idea is to sample platelets across several oil-immersion fields to get an average density, rather than relying on a single field. This sampling reduces the impact of uneven distribution or clumping on the smear and yields a more reliable estimate of the actual platelet concentration. Counting a practical number of fields strikes a balance between accuracy and efficiency: too few fields can give a skewed result if platelets aren’t evenly spread, while counting many more fields takes extra time without significantly changing the estimate. Once you have the average platelets per field, you apply a conversion factor to estimate the number of platelets per microliter. So the procedure uses a standard, reasonable number of oil-immersion fields to produce a dependable estimate.