APPENDIX D: MALARIA RAPID TEST & MICROSCOPY

MICROSCOPY

When done correctly, microscopic examination of thick and thin blood smears is the most reliable test for malaria. Blood smears are taken most often from a finger prick and a few drops of blood. Thick and thin blood smears allow direct visualization of parasites and their reproductive derivatives – schizonts in malaria. See U.S. Department of Defense. Special Operations Forces Medical Handbook. 2011.

- A thick blood smear is a drop of blood on a glass slide. Thick blood smears are most useful for detecting the presence of parasites, because they examine a larger sample of blood. (Often there are few parasites in the blood at the time the test is done).
- A thin blood smear is a drop of blood that is spread across a large area of the slide. Thin blood smears help providers discover what species of malaria is causing the infection.
- The two smears can work in tandem if a thick and thin smear is made. This method allows the provider to observe both thick and thin smears and find the blood density that is most likely to yield visualization of the parasite to the given observer.
- If a high index of suspicion exists for malaria in a given patient, but microscopy does not reveal an obvious malarial infection, serial thick and thin smears can be repeated every 8 or 24 hours depending on the severity of the case.

The thick and thin film should be air-dried, fixed with 100% (absolute) methanol, and allowed to dry before staining with 7.5% Giemsa stain for 15 minutes. Plasmodium parasites are always intracellular, and they demonstrate, if stained correctly, blue cytoplasm with a red chromatin dot (see images 1-4 below). Common errors in reading malaria films can be caused by platelets overlying a red blood cell, concern regarding missing a positive slide, and misreading of artifacts as parasites. The slide is best read by starting at the thin end of the slide and moving it towards the thick side until the RBCs are side by side, but NOT overlapping. This will give the observer the highest concentration of RBCs in view, giving him or her the highest probability of identifying the parasite. Move the slide along this plane of side-by-side RBCs to accurately rule out or in a malarial parasitic infection (Image 1). If the malaria parasite is identified, begin appropriate anti-malaria/anti-parasite treatment immediately in conjunction with the antibiotic therapies (minimum, better, best) mentioned above.