Rationale:

• Although a blood smear exam is the standard for malaria diagnosis, the sensitivity of this test is operator dependent; rapid diagnostic testing may complement this test.
• Rapid diagnostic tests do not quantify parasitemia and can only complement, rather than replace, the blood smear.
• Although commercially available tests are simple to use and interpret, they are not 100% sensitive, they may not detect Plasmodium species other than P. falciparum, and they will not detect other fever-causing blood parasites.

Evidence:

• Two types of rapid diagnostic tests are commercially available in the U.S. for research and development only. Both manufacturers currently are seeking FDA approval for the use of their tests in the diagnosis of malaria. (A previously available rapid diagnostic test, ParaSight F, is no longer manufactured.) The first type of test, represented by NOW® ICT Malaria Pf/Pv (Binax Inc., Portland, ME), is based on the detection of both P. falciparum histidine-rich protein 2 and a pan-Plasmodium antigen (aldolase). Although the NOW® ICT Malaria Pf/Pv test is highly sensitive and specific for malaria diagnosis (66; 67), it does have limitations. First, tests based on detection of P. falciparum histidine-rich protein 2 cannot be used to monitor therapeutic responses because this antigen persists up to 28 days after treatment (68). Second, this test cannot distinguish between P. vivax, P. ovale, and P. malariae and cannot distinguish the single P. falciparum species infection from mixed-species infections. Although these distinctions are not necessary for treatment of blood stage infections, determining whether P. falciparum is accompanied by P. vivax or P. ovale may be important in assessing the need for eradicating liver stages (hypnozoites) with primaquine.
• The second type of test, represented by OptiMAL® (DialMed; under license from Flow Inc., Portland, OR) is based on the detection of Plasmodium lactate dehydrogenase. The OptiMAL® assay detects P. falciparum and P. vivax infections in travelers with high sensitivity and specificity (67; 69; 70; 71). Test sensitivity under field conditions may be somewhat lower (72). One advantage of the OptiMAL® assay is that the level of Plasmodium lactate dehydrogenase detected is proportional to parasitemia (73), allowing for monitoring of therapeutic responses (71).
• The NOW® ICT Malaria Pf/Pv test and OptiMAL® assay share some disadvantages. Both tests may miss some P. falciparum and P. vivax infections if parasitemias are low (i.e., <100 P. falciparum/µL or <1000 P. vivax/µL). Both tests detect P. ovale and P. malariae infections with a relatively low sensitivity (range, 50% to 70%) (66; 71); however, these infections are relatively infrequent among U.S. travelers and are not associated with high morbidity or mortality in this population. The association of P. malariae with tropical splenomegaly and nephrotic syndrome is important in the tropics, however. Both tests commonly (3% to 26%) yield false-positive results in individuals with rheumatoid factor (69; 74).

Comments:

• None.