Rapid diagnosis of severe malaria based on the detection of Pf-Hrp-2 antigen

Abstract

Blood samples collected from 34 patients with severe malaria who were involved in antimalarial treatment studies were tested with rapid dipstick assay (Rapid Test Malaria, RTM from Quorum Diagnostics Inc., Vancouver, BC, Canada), based on the detection of Histidine Rich Protein (HRP-2) of Plasmodium falciparum. This was compared with the conventional Giemsa stained thin and thick blood smears. The study was done from March 1998 to May 1998, at the Basic Research Laboratory of the Faculty of Medicine, Addis Ababa University. Comparable number of patients (n = 32) with various diagnosis other than falciparum malaria were used as controls. The rapid dip-stick assay was positive in 31 among 34 of the severe malaria cases with sensitivity of 91.2%, specificity of 93.7%, positive predictive value (PPV) of 93.9% and negative predictive value (NPV) of 90.9%. The three cases missed by the RTM, had parasitemia of 66,000, 44,000, and 40,000/microL of blood which might be due to genetic heterogeneity of the HPR-2 expression. Among the controls, there were 2 false positive cases which may be as a result of persistent HPR-2 antigen after the clearance of peripheral parasitemia. The dip-stick method is a very quick, sensitive and specific diagnostic tool with limits of detection comparable or better than those provided by the light microscopy. The simplicity of the technique makes this method more applicable in the resource deprived laboratories of developing countries provided the kit is affordable for large scale use.