The most sensitive among the following tests for diagnosis of malaria is -

Investigations Giemsa-stained thick and thin blood films should be examined whenever malaria is suspected. In the thick film, erythrocytes are lysed, releasing all blood stages of the parasite. This, as well as the fact that more blood is used in thick films, facilitates the diagnosis of low-level parasitaemia. A thin film is essential to confirm the diagnosis, species and, in P. falciparum infections, to quantify the parasite load (by counting the percentage of infected erythrocytes). P. falciparum parasites may be very scanty, especially in patients who have been paially treated. With P. falciparum, only ring forms are normally seen in the early stages; with the other species, all stages of the erythrocytic cycle may be found. Gametocytes appear after about 2 weeks, persist after treatment and are harmless, except that they are the source by which more mosquitoes become infected. Immunochromatographic rapid diagnostic tests (RDTs) for malaria antigens, such as OptiMAL (which detects the Plasmodium LDH of P. falciparum and vivax) and Parasight-F (which detects the P. falciparum histidine-rich protein 2), are extremely sensitive and specific for falciparum malaria but less so for other species. They should be used in parallel with blood film examination but are especially useful where the microscopist is less experienced in examining blood films (e.g. in the UK). They are less sensitive for low-level parasitaemia and positivity may persist for a month or more in some individuals. The QBC Malaria Test is a fluorescence microscopy-based malaria diagnostic test that is also widely used. DNA detection (PCR) is used mainly in research and is useful for determining whether a patient has a recrudescence of the same malaria parasite or a reinfection with a new parasite. Diagnostic uses Quantitative buffy coat (QBC) is a laboratory test to detect infection with malaria or other blood parasites. In such cases the medical technologist may obtain a buffy coat, from which a blood smear is made. Ref Harrison20th edition pg 1056