The diagnosis of blood parasites involves examination and identification in blood smear preparations as well as the detection of their antigens or products in blood. Different stages of the parasite life cycle can be detected in the blood of victims through microscopic examination of thick and thin blood smears, after staining with appropriate dyes such as the Romanowsky stains.
For many years, parasitic identification in blood slides has been considered the gold standard. It is therefore important to understand the creation of thick and thin smear.
The difference in diagnostic sensitivity of the two smears is that the thick smear involves the concentration of more blood volume thus increasing chances of parasite detection while thin smears are used in the identification of parasite species as they are spread well on the slide and are easy to identify. These smears can also be used in the examination of Quantitative Buffy Coat tests.
After blood collection or finger pricking, use a clean slide and take 3 drops of blood for thick smear and one drop for thin smear about one centimeter apart. Using a glass slide with smooth edges, spread the blood and allow it to air dry. Make sure to mark the slides with a pencil either diamond or graphite with the sample number for identification and reporting.
Common Mistakes in Smear Preparation
- Too little blood on the slide
- Chipped or rough edges on the spreader
- Pushing the spreader too quickly
- Hesitation on the forward motion of the slide
- Elevated blood lipids; or dirty/ greasy slide
- Uneven pressure on the slide
- Time delays