Canadian Society for Medical Laboratory Science (CSMLS) Practice Exam

What causes the appearance of holes in a blood smear?

1. Dirty slide

2. Air bubbles

3. Over-diluted sample

4. Incorrect staining

The correct answer is: Dirty slide

The appearance of holes in a blood smear can indeed be caused by a dirty slide. When preparing a blood smear, the glass slide must be clean to ensure that the cells spread evenly and are visible for analysis. Any residue, debris, or contaminants on the slide can interfere with the integrity of the sample, leading to the formation of voids or "holes" where red blood cells are either absent or poorly distributed. This can create a misleading representation of the blood composition, affecting the diagnostic process. In contrast, the other factors listed typically do not produce the same appearance of holes. Air bubbles might cause localized areas of disruption, but they would not create empty spaces in the same way as a dirty slide would. An over-diluted sample could result in a sparse distribution of cells, but not necessarily visible holes. Incorrect staining mainly affects the coloration of the cells rather than causing actual gaps in the smear. Thus, a dirty slide is the primary factor leading to the observation of holes in a blood smear.