Comparison of a rapid field immunochromatographic test to expert microscopy for the detection of Plasmodium falciparum asexual parasitemia in Thailand

We assessed a rapid, Plasmodium falciparum histidine rich protein 2 (PfHRP2 )-based immunochromatographic test (ICT Malaria Pf Test(TM)), for detection of asexual P. falciparum parasitemia in 551 subjects in three groups: (1) symptomatic patients self-referring for diagnosis, (2) villagers in a scree ning survey, and (3) patients recently treated for P. falciparum malaria. E xpert light microscopy was the reference standard. ICT test performance was similar for diagnostic and screening modes. Four findings emerged: (1) tes t sensitivity correlated directly with parasite density, (2) test band inte nsity correlated directly with parasite density, (3) persistent test positi vity after parasite clearance precludes its use for monitoring early therap eutic responses, and (4) a false negative test at 18000 parasites/mu l is u nexplained. We conclude that a strong positive ICT test is highly predictiv e of falciparum asexual parasitemia for the diagnosis of new cases of falci parum malaria in Thailand, but a negative test result is inadequate to excl ude parasitemia < 300/mu l, and in some instances, even a higher parasitemi a. (C) 1999 Elsevier Science B.V. All rights reserved.