Infectious Disease
Malaria
Malaria rapid diagnostic tests (RDTs) detect Plasmodium antigens in a fingerprick or venous whole blood sample, giving a qualitative positive or negative result within minutes at the bedside. They are an adjunct to, not a replacement for, blood film microscopy, which remains the reference method for confirmation and parasite quantification.
Why it is measured
Malaria is a medical emergency in which prompt antigen detection supports timely treatment decisions, particularly where microscopy is not immediately available. Falciparum malaria can deteriorate rapidly, so early identification of a positive result is operationally important.
| Typical range | Qualitative result, reported as Negative, Positive or Invalid; the expected result in an unaffected adult is Negative, meaning no Plasmodium antigen detected. Antigen RDTs do not give a numeric concentration, and the antigen targets vary by product: an HRP-2 line indicates P. falciparum, whereas pan-pLDH or aldolase lines detect all Plasmodium species, so the combination of lines is used to suggest non-falciparum or mixed infection. Note that HRP-2 can remain detectable for days to several weeks after successful treatment, so interpretation varies by method and antigen target. |
|---|---|
| Sample | Capillary (fingerprick) or venous whole blood; venous samples are commonly EDTA-anticoagulated, while capillary blood is usually applied directly. A few microlitres are added to the cassette well with the supplied buffer. |
| Turnaround | Approximately 15 to 20 minutes, read within the manufacturer-specified time window. |
Point of care devices that report it
- Abbott BinaxNOW Malaria
- Abbott SD Bioline Malaria Ag P.f/Pan
- Access Bio CareStart Malaria HRP2/pLDH Combo
- Abbott NxTek Eliminate Malaria Ag Pf
- Wondfo One Step Malaria P.f/Pan Antigen Test
- RapiGEN BIOCREDIT Malaria Ag
Questions, answered
Does a negative malaria RDT rule out malaria?
No. RDTs can miss low parasite densities, may not detect non-falciparum species if the test targets only P. falciparum, and can be affected by HRP-2 gene deletions. A negative result with ongoing clinical suspicion should be followed by blood film microscopy, often repeated, alongside clinical assessment per local protocol.
Why can an RDT stay positive after treatment?
HRP-2 antigen can persist in the blood for days to several weeks after the parasites have cleared, so an HRP-2 based test may remain positive even when treatment has worked. Persistence alone does not indicate treatment failure; microscopy or pLDH-based tests, which clear more quickly, are more useful for assessing response.
Which Plasmodium species do these tests detect?
It depends on the antigen targets printed on the device. An HRP-2 line is specific to P. falciparum, whereas a pan-pLDH or aldolase line signals any Plasmodium infection and is used to flag non-falciparum or mixed infection without precisely identifying the species. Always check the species coverage stated for the specific test in use.