# Impact of age and immune status on the accuracy of rapid diagnostic tests for visceral leishmaniasis in Brazil

## TL;DR

This study shows that rapid diagnostic tests for visceral leishmaniasis are less accurate in young children and HIV-positive patients in Brazil.

## Contribution

The study evaluates the performance of three RDTs for VL in relation to age and immune status, revealing critical limitations in specific patient groups.

## Key findings

- RDTs showed lower sensitivity in children under 3 years old and HIV co-infected individuals.
- The agreement between observers and test repeatability was excellent for all three RDTs.
- Performance variation highlights the need for alternative diagnostics in vulnerable groups.

## Abstract

Visceral leishmaniasis (VL) represents a significant public health concern due to its high case-fatality, which poses the challenge of a timely and accurate diagnosis. Antibody-based rapid diagnostic tests (RDTs) have emerged as a disruptive innovation in recent years, by offering a diagnosis in the field, at low cost, easy to perform and with results in a few minutes. However, their performance can vary across regions and different subgroups, particularly in immunocompromised individuals. This study aimed to assess the accuracy of VL RDTs registered with the Brazilian national regulatory agency, or available through the PAHO strategic fund, considering diverse patient profiles.

Three commercially RDTs were identified LSH Ab Eco Teste, Leishmaniasis VH Bio, and Kalazar Detect and evaluated using a well characterized panel of serum samples (n = 300) from suspected VL patients from different Brazilian regions. Sensitivity, specificity, and accuracy were determined for different patient’s ages and HIV coinfection status. Overall, RDTs exhibited lower sensitivity in children under 3 years old and HIV co-infected individuals compared to those over 3 years without HIV co-infection (p < 0.05). The agreement (Cohen’s kappa coefficient) between observers (reproducibility) and intra-test (repeatability) for all three commercial kits was excellent.

While RDTs offer desirable advantages in terms of access to diagnoses, variation on their performance imposes limits on their implementation. The performance of RDTs for VL exhibits significant differences related to age and immune status.

Visceral leishmaniasis (VL) is a severe disease that affects thousands of people worldwide, particularly in areas with limited healthcare resources. Early and accurate diagnosis is crucial because VL can be fatal if left untreated. Rapid diagnostic tests (RDTs) have been developed to offer fast, simple, and affordable diagnoses, making them particularly useful in remote regions. However, these tests don’t always perform equally well across different patient groups, such as children and individuals with weakened immune systems, including those co-infected with HIV. This study evaluated three commercially available RDTs for VL, focusing on their accuracy across diverse patient profiles in Brazil. The results showed that while these tests are generally reliable, they are less sensitive in children under 3 years of age and in HIV-positive patients. These findings highlight the importance of considering patient characteristics when using RDTs in the field, as certain groups may require alternative or supplementary diagnostic approaches to ensure accurate detection of the disease.