A new Cochrane Systematic Review shows that when tested in scientific studies, RDTs are accurate and sensitive in detecting Plasmodium falciparum malaria.
Fever is common in malarial areas, and getting the diagnosis right and treating correctly helps save lives, particularly in children. The World Health Organization (WHO) now recommends that all patients with fever and suspected of having malaria undergo a malaria test before any treatment begins. This ensures that highly effective antimalarial drugs such as artemisinin-based combination treatments (ACTs) are properly used, and that infections that are not malaria are treated correctly too (for instance, antibiotics for bacterial infections). If people don’t get the right treatment for their infection they may suffer adverse effects unnecessarily and it also wastes resources and over time can promote resistance to available drugs.
Standard diagnosis of malaria in the past has depended on blood microscopy, but this requires a technician and a laboratory, and is often not feasible for basic health services in many areas. Sometimes in research studies, another technique called polymerase chain reaction (PCR) is used, but again this requires equipment and trained staff, and cannot be used routinely. Technological advances have led to rapid diagnostic tests (RDTs) for malaria. These detect parasite-specific antigens in the blood, are simple to use, and can give results as a simple positive or negative result, within 15 minutes.
The Cochrane infectious Diseases Group completed this complex review, which summarises studies comparing RDTs with a reference standard, usually microscopy. It includes 74 studies of patients attending ambulatory health facilities with malaria symptoms from P. falciparum endemic areas. RDTs are categorized into types according to the malaria antigens they detect. Types 1 to 3 include histidine-rich protein-2 (HRP-2) (from P. falciparum) either by itself or with other antigens, and types 4 and 5 include plasmodium lactate dehydrogenase (pLDH) (from P. falciparum) either by itself or with other antigens.
Most studies identified for this review were carried out on Type 1 (HRP-2) and Type 4 (pLDH) tests. All RDTs performed reasonably well, and it can be concluded that with their high sensitivity and specificity, RDTs can replace microscopy for diagnosing P. falciparum malaria. When comparing different types of RDTs, the authors found that HRP-2 -based tests (such as the Type 1 tests) tended to be more sensitive and were significantly less specific than pLDH-based tests (such as the Type 4 tests). As a consequence, type 1 tests miss less cases of P. falciparum malaria than type 4 tests but give more false positives, resulting in more people being treated for malaria when they are not infected.
As new RDTs are developed and become available, future studies should include comparisons between new tests and commonly-used Type 1 and/or Type 4 RDTs, done in the same patients. More research on how to effectively incorporate the use of RDTs within routine clinical practice is also needed.
The Cochrane Infectious Diseases Group (CIDG) is a partner of the Effective Health Care Research Consortium, funded by DFID. The editorial base of the CIDG is located at the Liverpool School of Tropical Medicine. CIDG has been preparing systematic reviews on the benefits and harms of healthcare interventions for infectious diseases, particularly malaria, tuberculosis, diarrhoea, and tropical diseases, since 1994.