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Table 1 Blood smears classification criteria (Adapted from Kiggundu et al.[15])

From: Impact of a training course on the quality of malaria diagnosis by microscopy in Angola

Classification Criteria
Thick blood smear Thin blood smear
Bad - Smear too big (diameter greater than 1 cm) or too small (diameter less than 0.5 cm); - Smear too big (more than half of the slide) or too small (smaller than 0.5 cm);
- Smear very close from the edge of the slide (less than 1 cm) which enables the use of immersion oil; - Smear spread unevenly with patchy distribution, streaky and with many tails (greasy slides or edge of the spreader slide chipped);
- Very thick smear (fine print cannot be read through it); - Very thick smear that fine print cannot be read through it or too thin with few red blood cells;
- Poorly stained (red blood cells are not lysed and parasites have a green, red, or blue colour). - Many red blood cells lysed and lightly stained cells (red and white blood cells) and parasites.
Satisfactory Smear well-made regarding size and location but moderately stained (red blood cells are partially lysed and parasites are lightly stained). Smear well-made regarding size and location but moderately stained (red blood cells are partially lysed and parasites are lightly stained).
Good - Smear round in shape with a diameter of approximately 1 cm; - Smear with the right dimension (half of the slide leaving space for thick blood);
- Smear at least 1 cm away from the edge of the slide; - Smear spread evenly (without patchy or streaky distribution);
- Smear density that fine print can be read through it; - Smear density that fine print can just be read through it;
- Smear with all of the red blood cells lysed, and the malaria parasites are well-exposed with a bluish pink coloration. - Smear with intact red blood cells and pink coloration, intact white blood cells properly stained, and malaria parasites are well-exposed with a bluish pink coloration.