page_title: Blood film
section_title: Malaria
hierarchical_section_title: Blood film / Malaria
caption_attribution_description: English: Synchronised cultures of the blood stages of Plasmodium falciparum.
context_page_description: A blood film—or peripheral blood smear—is a thin layer of blood smeared on a glass microscope slide and then stained in such a way as to allow the various blood cells to be examined microscopically. Blood films are examined in the investigation of hematological disorders and are routinely employed to look for blood parasites, such as those of malaria and filariasis.
context_section_description: The preferred and most reliable diagnosis of malaria is microscopic examination of blood films, because each of the four major parasite species has distinguishing characteristics.  Two sorts of blood film are traditionally used.
  Thin films are similar to usual blood films and allow species identification, because the parasite's appearance is best preserved in this preparation.
  Thick films allow the microscopist to screen a larger volume of blood and are about eleven times more sensitive than the thin film, so picking up low levels of infection is easier on the thick film, but the appearance of the parasite is much more distorted and therefore distinguishing between the different species can be much more difficult.
  From the thick film, an experienced microscopist can detect all parasites they encounter. Microscopic diagnosis can be difficult because the early trophozoites ("ring form") of all four species look identical and it is never possible to diagnose species on the basis of a single ring form; species identification is always based on several trophozoites.
  The biggest pitfall in most laboratories in developed countries is leaving too great a delay between taking the blood sample and making the blood films.  As blood cools to room temperature, male gametocytes will divide and release microgametes: these are long sinuous filamentous structures that can be mistaken for organisms such as Borrelia. If the blood is kept at warmer temperatures, schizonts will rupture and merozoites invading erythrocytes will mistakenly give the appearance of the accolé form of P. falciparum. If P. vivax or P. ovale is left for several hours in EDTA, the buildup of acid in the sample will cause the parasitised erythrocytes to shrink and the parasite will roll up, simulating the appearance of P. malariae. This problem is made worse if anticoagulants such as heparin or citrate are used.  The anticoagulant that causes the least problems is EDTA. Romanowsky stain or a variant stain is usually used. Some laboratories mistakenly use the same staining pH as they do for routine haematology blood films (pH 6.8): malaria blood films must be stained at pH 7.2, or Schüffner's dots and James's dots will not be seen.
  Immunochromatographic capture procedures (rapid diagnostic tests such as the malaria antigen detection tests) are nonmicroscopic diagnostic options for the laboratory that may not have appropriate microscopy expertise available.
caption: Blood films showing various developmental stages of the malaria parasite Plasmodium falciparum, stained with Wright stain and Giemsa stain.
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