Field trial of the RTM dipstick method for the rapid diagnosis of malaria based on the detection of Plasmodium falciparum HRP-2 antigen in whole blood.

The performance of the Quorum RapidTest Malaria (RTM) dipstick method that detects Plasmodium falciparum histidine-rich protein-2 (PfHRP-2) antigen in whole blood was evaluated in a malaria endemic area. Results were compared with conventional Giemsa-stained blood films. Of 306 people tested 37.9% (116/306) were found to be parasitaemic; of these 66.4% (77/116) were P. vivax and 32.8% (38/116) were P. falciparum infections. There was only one (0.9%) mixed P. falciparum plus P. vivax infection. The RTM test was positive in 35/36 patients with P. falciparum identified on blood smear examination, resulting in a sensitivity of 97.2% [95% confidence interval (CI): 91.6-102.8%]. Specificity was 96.3% (95% CI: 93.9-98.6%). The RTM test had a positive predictive value of 77.8% (95% CI: 65.7-89.9%) and a negative predictive value of 99.6% (95% CI: 98.4-100.8%). Of the 10 false positives, seven reported recent malaria episode and treatment, indicating persistence of antigenaemia. If these were assumed truly infected, the positive predictive value is increased to 93.3% (95% CI: 85.8-100.8%). The RTM test was positive in all seven P. falciparum infections with gametocytes and one mixed infection, but was negative in all falciparum gametocytes and relapsing fever cases. All but one P. vivax infection gave negative result on the RTM test. The RTM test missed one patient with parasitaemia. The test is highly sensitive and specific requiring no instrument or trained personnel. It appears to be a very useful tool for rapid diagnosis of malaria, especially in the rural health institutions with limited diagnostic facilities.