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Full Blood Count Quiz
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What is the main purpose of spreading a blood film so that it is only one cell thick?
- A To allow the size, shape and colour of individual blood cells to be assessed You picked ✓
- B To allow white blood cells to be identified without the need for staining You picked ✕
- C To reduce the amount of Romanowsky stain needed to cover the slide You picked ✕
- D To enhance the chemical fixation of cells by methanol You picked ✕
- E To make abnormal cells stain more strongly than normal cells You picked ✕
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Incorrect
The answer is A: To allow the size, shape and colour of individual blood cells to be assessed
Explanation
Why A is correct
See Blood Films. Option A is correct. A blood film (or blood smear) is a thin layer of blood spread on a glass slide, fixed, stained and examined under the microscope to look at the shape and appearance of the blood cells. It is made by placing a drop of blood on a slide and drawing it out with a second slide held at an angle, which leaves a smear with a thicker head, a body and a thin, feathered tail. The part used for examination is the thin area near the tail, where the cells lie in a single layer, called the monolayer. In the thick head the cell density is about twice as high, and the cells are crowded together. In the monolayer the cells are separate, so the size, shape and colour of each cell can be judged. This is how abnormal red cells, abnormal white cells and platelet changes can be recognised. A simple memory aid is that a blood film is read in the thin part, not the thick part: if cells overlap you cannot see them properly.
- Monolayer: the thin area near the tail where cells lie in a single layer.
- Thick head: cells are crowded and overlap.
- Purpose: separate cells let their size, shape and colour be judged.
Why the other options are incorrect
- B. To allow white blood cells to be identified without the need for staining: A blood film still requires Romanowsky staining before white blood cells can be identified; the monolayer separates cells but does not make staining unnecessary. Your answer
- C. To reduce the amount of Romanowsky stain needed to cover the slide: The monolayer is used for cell assessment, not to reduce stain volume; the amount of stain needed is determined by covering the whole film, and the thin area is only part of it. Your answer
- D. To enhance the chemical fixation of cells by methanol: Methanol fixation is a separate step done after the film has dried. The thinness of the film does not improve how well the cells are fixed. Your answer
- E. To make abnormal cells stain more strongly than normal cells: Romanowsky stains colour all cells and their components using acidic and basic dyes; the monolayer does not cause abnormal cells to stain more strongly than normal cells. Your answer
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More questions from this set. Start the quiz to answer them and see each explanation.
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1
A blood film report describes red blood cells that show a large variation in size, but most cells retain a normal shape. Which term best describes this finding?
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2
When is a manual blood film most appropriately requested after an automated full blood count?
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