Test characteristics of two rapid antigen detection tests (SD FK50 and SD FK60) for the diagnosis of malaria in returned travellers

BACKGROUND: Two malaria rapid diagnostic tests were evaluated in a travel clinic setting: the SD FK50 Malaria Ag Plasmodium falciparum test (a two-band test) and the SD FK60 Malaria Ag P. falciparum/Pan test (a three-band test). METHODS: A panel of stored whole blood samples (n = 452 and n = 614 for FK50 and FK60, respectively) from returned travellers was used. The reference method was microscopy with PCR in case of discordant results. RESULTS: For both tests, overall sensitivity for the detection of P. falciparum was 93.5%, reaching 97.6% and 100% at parasite densities above 100 and 1,000/microl respectively. Overall sensitivities for Plasmodium vivax, Plasmodium ovale and Plasmodium malariae for the FK60 test were 87.5%, 76.3% and 45.2%, but they reached 92.6% and 90.5% for P. vivax and P. ovale at parasite densities above 500/microl. Specificities were above 95% for all species and both tests when corrected by PCR, with visible histidine-rich protein-2 lines for P. malariae (n = 3) and P. vivax and P. ovale (1 sample each). Line intensities were reproducible and correlated to parasite densities. The FK60 tests provided clues to estimate parasite densities for P. falciparum below or above 1,000/microl. CONCLUSION: Both the FK50 and FK60 performed well for the diagnosis of P. falciparum in the present setting, and the FK60 for the diagnosis of P. vivax and P. ovale at parasite densities > 500/microl. The potential use of the FK60 as a semi-quantitative estimation of parasite density needs to be further explored.