Fig. 4

Linearity and sensitivity of the VSG-based flow cytometric assay. a Representative graph of the Spearman’s rank correlation coefficients. Percentage of P. falciparum-infected erythrocytes was obtained from VSG-based flow cytometry (Y-axis) and from Giemsa staining of thin blood film (X-axis). Three independent analyses were performed that revealed a range of infected erythrocytes of 0.01–6.4%, as shown in the table. b Sensitivity of VSG-based flow cytometry. Culture of P. falciparum was diluted to 0.001% parasitaemia, which is the limit of detection in routine microscopic diagnosis [20], and then analysed by flow cytometry. Representative flow cytometric profile and data are shown as mean ± SD. The graph shows a comparison of parasitaemia detected by standard microscope and VSG+ cells detected by flow cytometry. c Reproducibility of the VSG-based flow cytometric assay for low parasitaemia culture. Three independent settings of P. falciparum culture were diluted to 0.01% parasitaemia and analysed using flow cytometry. Unstained, P. falciparum-infected erythrocytes were used as control. VSG, ViSafe Green; FSC-A, forward scatter-area