Sunday, March 25, 2012

Class Note: Laboratory Diagnosis of Malaria

Once malaria is suspected on clinical grounds, it is mandatory to obtain the laboratory confirmation of the presence of malaria parasites in the patient’s organism, whenever possible. The diagnosis of malaria may in fact be pursued by the direct demonstration of the parasite whole cell or of parasite’s nucleic acid or products in the blood (direct diagnosis) or by the demonstration of the patient’s immune response to the infection (indirect diagnosis or immunodiagnosis)

The direct demonstration of the whole parasitic cell may be accomplished by several methods, from the old and simple (but still golden standard!) direct microscopic observation of stained blood specimen to the more recent and sophisticated concentration and staining techniques (Quantitative Buffy Coat ®, acridine orange method). Finally, the detection of the presence of the genome of the parasite is now possible by the Polymerase Chain Reaction (PCR) technique. New and sensitive immunological methods to detect P. falciparum antigens have yielded promising results for the individual diagnosis of malaria infection.

The evidence of seric specific antibodies is of little, if any, diagnostic value in endemic malaria
areas but may provide important information in epidemiological studies and, in some selected
setting, in blood donor screening

Rapid and accurate diagnosis of malaria is integral to the appropriate treatment of affected individuals and is preventing the further spread of infection in the community.

a. Microscopy
Microscopic examination remains the “gold standard” for laboratory confirmation of malaria. Microscopy is an established, relatively simple technique that is familiar to most laboratorians. Any laboratory that can perform routine hematology test is equipped to perform a thick and thin malaria smear. Within few hours of collecting the blood, the microscopy test can provide valuable information. First and foremost, it can determine that malaria parasites are present in the patients blood.

Once the diagnosis is established, usually by detecting parasites in the thick smear, thin smear can be examined to determine the malaria species and the parasitemia, or the percentage of the patients red cells that are infected with malarial parasites.

Blood specimen collected from the patient is spread as a thick or thin blood smear, stained with a romanovsky stain (most often Giemsa), and examined with 100x oil immersion objective. Visual criteria are used to detect malaria parasites and to differentiate (when possible) the various species.

View blog post about Rapid Diagnostic Tests for Malaria Here

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