Notice to Readers: Malaria Rapid Diagnostic Test

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On June 13, 2007, the Food and Drug Administration approved BinaxNOW^® Malaria (Inverness Medical Professional Diagnostics, Scarborough, Maine), the first malaria rapid diagnostic test (RDT) authorized for use in the United States. Malaria RDTs, which detect circulating malaria-specific antigens, already are available in other countries and often are used in settings where malaria microscopy is not available. In the United States, use of the RDT can decrease the amount of time required to determine whether a patient is infected with malaria.

BinaxNOW^® Malaria is approved for use by hospital and commercial laboratories, not by individual clinicians or by patients themselves; however, the manufacturer is planning to seek a Clinical Laboratory Improvement Amendments waiver for point-of-care use by clinicians. The RDT detects two different malaria antigens: HRP2, which is specific to Plasmodium falciparum, and a malaria aldolase found in all four human species of malaria parasites. Although the test can identify P. falciparum, it cannot distinguish between Plasmodium vivax, Plasmodium ovale, or Plasmodium malariae or detect mixed infections. The manufacturer recommends that the laboratory maintain a supply of blood containing P. falciparum for use as a positive control (1).

Use of a malaria RDT does not eliminate the need to examine thick and thin blood smears for the presence of malaria parasites. The RDT might not be able to detect infections with lower concentrations of malaria parasites, and data are insufficient to determine the ability of this test to detect the two less common species of malaria parasite, P. ovale and P. malariae. Therefore, all negative RDT results should be followed by microscopy to confirm the results and accurately identify the species.

Although malaria treatment should be initiated after receipt of positive RDT results, these results also should be followed by microscopy. In cases of nonfalciparum malaria, microscopy is needed to determine the species of malaria parasite. In addition, because the result of the RDT is qualitative and not quantitative, it cannot be used to determine initial parasite density or the parasitologic response to therapy. Therefore, serial microscopy is needed to quantify the proportion of red blood cells that are infected, an important prognostic indicator that can be used to monitor response to therapy.

High-quality malaria microscopy is not always immediately available in every clinical setting. Although thick and thin blood smears should be examined immediately, in some health-care settings, blood smears are either saved until a qualified person is available to perform malaria microscopy or sent to commercial or reference laboratories. These practices have resulted in delays in diagnosis and initiation of appropriate management. Clinicians should be aware that certain hospitals and laboratories might offer RDT, which can aid the rapid diagnosis of malaria and result in prompt therapeutic intervention.

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