New study evaluates accuracy of rapid diagnostic tests for malaria

The paper has been published in Malaria Journal. 

Researchers from the Indian Council of Medical Research (ICMR)-National Institute of Malaria Research (NIMR) carried out malaria surveillance in 12 sites across India, and evaluated the performance of RDTs against microscopy, the gold standard for confirming malaria.

In field settings, RDTs provides a simple and easy approach for malaria diagnosis. These tests need a finger prick blood test, and when the blood is applied to a test strip, it interacts with a dye-labelled malaria antibody, with a visible line indicating a positive test appearing if malaria parasites are present. Similar to at-home COVID antigen testing, the tests can be done without any medical training. 

The research team from ICMR-NIMR carried out the surveillance, and in collaboration with the Infectious Diseases Data Observatory assessed the diagnostic performance of the RDTs. Researchers tested 10,290 febrile participants using both RDTs and microscopy. 

The RDTs identified a total of 1,516 malaria cases, while microscopy found only 1,436. Crucially, 43 subjects who tested RDT negative were found to have malaria on microscopic examination. 

In particular, the accuracy of the RDT was lower for participants with P. vivax  malaria – something that the researchers say warrants further investigation. 

Accurate detection important

In India, both P. falciparum and P. vivax malaria remain in circulation, so accurate detection of both malaria parasite species remains crucial for prompt and accurate treatment and reducing onward transmission.

Early and accurate diagnosis of malaria is one of the cornerstones of global malaria control and elimination efforts. While microscopy of peripheral blood smears remains the best method for malaria diagnosis, RDTs can be used where microscopy is not feasible, particularly in remote areas with limited healthcare access: in 2022, national malaria programmes distributed approximately 345 million RDTs worldwide, with 12.1 million RDTs distributed in the WHO South-East Asia region.

However, several diagnostic-related challenges exist or have recently emerged, including failure to detect a low density of parasites in the blood and limited accuracy for detecting mixed infections of both P. vivax and P. Falciparum.  

Another emerging challenge is the rise of ‘diagnostic-resistant’ malaria parasites that carry partial or complete deletions of the pfhrp2 and pfhrp3 genes. These genes produce the HRP2 protein targeted by many rapid diagnostic tests, so when they are missing, the tests can falsely appear negative even though parasites are present.

ICMR-NIMR’s Dr Praveen Bharti, the study lead scientist said: “A key concern is the poor sensitivity of rapid diagnostic tests in detecting P. vivax and mixed infections. 

“Because the treatments for P. falciparum and P. vivax malaria differ, missed diagnoses can result in inadequate patient care. Timely and systematic monitoring of performance of these RDTs and assessing pfhrp2/3 gene deletions is therefore critical to guide optimal diagnostic strategies.” 

“Overall, this study demonstrates that caution should be warranted regarding the accuracy of the diagnostic tests for Vivax malaria.”

Dr. Prabin Dahal from IDDO said: “Large scale surveillance project like this remain important not only to support national programs in pinpointing high-burden areas, but also for monitoring the emerging challenge of diagnostic resistance. 

“The analysis of pfhrp2/3 genes deletion assays which is nested within this surveillance study, is currently progressing and these results should help policymakers to guide resource allocation and strengthen strategies in the fight against malaria.”

Read the paper