Rapid diagnostic tests (RDT) for malaria, based on the detection in blood of antigens of the malarial parasites, may serve to support a clinical diagnosis of malaria and, in certain clinical situations, may provide a faster, simpler...
moreRapid diagnostic tests (RDT) for malaria, based on the detection in blood of antigens of the malarial parasites, may serve to support a clinical diagnosis of malaria and, in certain clinical situations, may provide a faster, simpler alternative to the examination of bloodsmears for malarial parasites. Cerebral malaria, an acute encephalopathy complicating human infection with Plasmodium falciparum, is a medical emergency where prompt differential diagnosis, among patients presenting with acute encephalopathy accompanied by fever, may be life-saving. In the present, hospital-based, observational study, the performance characteristics of the Paracheck Pf test (Orchid Biomedical Systems, Verna, Goa, India), an RDT based on a two-site, sandwich immuno-assay for the detection of P. falciparum-specific histidine-rich protein 2 (HRP-2), were evaluated against bloodsmear examination. The Paracheck Pf dipsticks were used to identify the cases of cerebral malaria among the 209 subjects, all of whom had acute febrile encephalopathy (i.e. fever with altered sensorium of (7 days’ duration) . The subjects were investigated as they attended one of two tertiary-care centres in the north Indian state of Uttar Pradesh: King George’s Medical University (KGMU) in Lucknow, or Baba Raghav Das Medical College in Gorakhpur. A patient presenting with acute febrile encephalopathy who was found bloodsmearpositive for P. falciparum was considered to be a confirmed case of cerebral malaria (Roman, 1991). Each RDT was performed as a bedside procedure, within 24 h of the patient’s admission, by a person specifically trained in its use for the present study. The test, which was purchased in its ‘device’ presentation (with the cassette device and a sample-applicator pipette for a single test sealed together in a plastic pouch), was performed according to its manufacturer’s instructions. The dipstick ‘cassette device’ was removed from the pouch and laid flat on the patient’s bedside table. A sample of whole blood was then collected from the patient, from a fingerprick or by venipuncture. Part of this sample was used to make smears (see below) but a 5-ml subsample of it was applied to the sample pad, in the well marked ‘A’ on the cassette, using the disposable plastic dispenser provided. Six drops (about 300 ml) of clearing buffer were then added to well ‘B’. The result was read after 15 min, a sample giving a distinct pink band in the ‘test window’ as well as a pink band in the ‘control window’ being considered RDT-positive for P. falciparum. Thin and thick bloodsmears, prepared at the same time as the RDT was performed, were stained with Leishman and Giemsa stain, respectively. All of the bloodsmears were examined for malarial parasites at the KGMU, by two microscopists who were unaware of the RDT results. A bloodsmear was only considered positive for P. falciparum if both microscopists reported seeing at least one ‘convincing’ asexual form of this parasite in the smear. Levels of parasitaemia (asexual stages/ml) were estimated from the thick smears, by counting asexual stages Annals of Tropical Medicine & Parasitology, Vol. 101, No. 1, 85–87 (2007)
