What objective magnification should be used to examine the heartworm direct smear?

What objective magnification should be used to examine the heartworm direct smear?

• A. 4x
• B. 10x
• C. 40x
• D. 100x

Answer: (B)

Scanning a heartworm direct smear is all about quickly spotting motile microfilariae. Using a low-power objective around 10x gives a wide field of view, so you can survey many cells and catch movement if microfilariae are present. Higher magnifications narrow the field and make tracking moving organisms slower and harder, which isn’t efficient for initial detection. Very low power like 4x lacks enough resolution to distinguish slender microfilariae from debris, and high power such as 40x or 100x is typically reserved for detailed morphology on fixed slides, not for screening a live smear. So, the best choice for examining a heartworm direct smear is 10x.

Scanning a heartworm direct smear is all about quickly spotting motile microfilariae. Using a low-power objective around 10x gives a wide field of view, so you can survey many cells and catch movement if microfilariae are present. Higher magnifications narrow the field and make tracking moving organisms slower and harder, which isn’t efficient for initial detection. Very low power like 4x lacks enough resolution to distinguish slender microfilariae from debris, and high power such as 40x or 100x is typically reserved for detailed morphology on fixed slides, not for screening a live smear. So, the best choice for examining a heartworm direct smear is 10x.