Performance and usability evaluation of three LDH-based malaria rapid diagnostic tests in Kédougou, Senegal

Abstract

Background: The emergence of pfhrp2/3-deleted parasites threatens histidine-rich protein 2 (HRP2)-based malaria rapid diagnostic test (RDT) performance. RDTs targeting Plasmodium falciparum (Pf) lactate dehydrogenase (LDH) may address current product limitations and improve case management.

Objectives: To evaluate the performance and usability of three LDH-based RDTs in febrile patients.

Methods: A cross-sectional diagnostic accuracy study was conducted in Kédougou, Senegal. Capillary blood was tested using the SD Bioline Ag Pf (#05FK50) and three LDH-based RDTs: BIOCREDIT Malaria Ag Pf (pLDH), BIOCREDIT Pf (pLDH/HRPII), and BIOCREDIT Pf/Pv (pLDH/pLDH) (Rapigen Inc., Republic of Korea). Venous blood was collected to repeat the BIOCREDIT RDTs and conduct microscopy. Frozen venous specimens were tested using a reference PCR assay. A quantitative multiplex malaria antigen assay measured antigen concentration. RDT performance was determined and analyzed as a function of antigen concentration distribution. Usability of the Pf-only BIOCREDIT tests was evaluated using a questionnaire.

Results: 154/220 participants (70%) were Pf-positive by PCR. The Pf (pLDH/HRPII) test demonstrated the highest sensitivity at 78% (70.9%-84.5%); specificity was 89% (79.4%-95.6%). All RDTs performed better than microscopy (53% sensitivity). RDTs performed better when compared to antigen concentration over PCR results. Improved sensitivity of the Pf (pLDH/HRPII) test was driven by the HRP2 line. Line intensity correlated with antigen concentration. Predicted sensitivity using the analytical limit of detection (LOD) was comparable to observed sensitivity. RDTs demonstrated acceptable usability.

Conclusions: Both HRP2 and LDH contributed to the sensitivity of the best-performing Pf-RDT. RDT analytical LODs can be used to predict performance in populations with known antigen concentrations.

Keywords: Malaria; diagnosis; histidine rich protein 2; lactate dehydrogenase; rapid diagnostic test.

Figure 1.

Box plots of (A) HRP2 and (B) pfLDH antigen concentration distributions as a function of parasite density in PCR-confirmed cases. Results by line from the BIOCRDIT Pf (pLDH/HRPII) test are indicated in color. Positive test lines are shown in red, and negative test lines are shown in blue for the HRP2 line and pfLDH line in panels A and B, respectively.

Figure 2.

HRP2 concentration plotted against PfLDH for clinical specimens. PCR-confirmed P. falciparum specimens are shown as filled triangles. PCR-negative specimens are represented as an open triangle. Test line results from the BIOCREDIT Pf (pLDH/HRPII) test are represented in color: red for HRP2-positive specimens, blue for LDH-positive specimens, and purple for specimens positive on both lines (Panel C).

Figure 3.

Correlation between antigen concentration and line intensity (0 is a negative test result, 1–15 are positive test results) on the BIOCREDIT Pf (pLDH/HRPII) RDT. Panel A shows the intensity of the HRP2 line on the RDT plotted against the HRP2 concentration. Panel B shows the intensity of the LDH line on the RDT plotted against LDH concentration. Dotted lines indicate the concentration at which line intensity is weakly visible (score of 1).