# Evaluation of a Fluorescence Immunoassay-Based IGRA for Latent Tuberculosis Diagnosis: A Simplified, Cost-Effective Alternative

## TL;DR

A new, low-cost fluorescence immunoassay for diagnosing latent tuberculosis shows strong agreement with existing tests and could be useful in resource-limited areas.

## Contribution

The study introduces and evaluates a simplified, cost-effective fluorescence immunoassay for latent tuberculosis diagnosis.

## Key findings

- The ichroma IGRA-TB showed 91.9% agreement with QuantiFERON-TB Gold Plus.
- It had acceptable sensitivity (69.0%) compared to a reference standard.
- The assay is suitable for near-point-of-care use in resource-limited settings.

## Abstract

Approximately 25% of the global population is estimated to have latent tuberculosis infection (LTBI), with a 5–10% lifetime risk of progression to active disease. Although interferon-gamma release assays (IGRAs) are widely used for LTBI diagnosis, their high cost and operational complexity limit large-scale implementation in resource-limited settings. This study evaluated the diagnostic performance of a low-complexity, rapid, fluorescence-based point-of-care assay, ichroma IGRA-TB, for LTBI detection. A total of 300 participants enrolled at TB Screening and Treatment Centers and the Dhaka Hospital of icddr,b were categorized as healthy controls (n = 130), household contacts of TB patients (n = 70), GeneXpert MTB/RIF Ultra-positive active TB patients (n = 80), or individuals with a previous history of TB (n = 20). ichroma IGRA-TB was compared with QuantiFERON-TB Gold Plus (QFT-Plus) across all groups. Overall agreement between ichroma IGRA-TB and QFT-Plus was 91.9%, with a Cohen’s kappa of 0.83, indicating almost perfect concordance. Using culture as a surrogate reference standard, QFT-Plus demonstrated higher sensitivity (74.6%) than ichroma IGRA-TB (69.0%). Overall, ichroma IGRA-TB demonstrates high agreement with QFT-Plus and acceptable sensitivity, supporting its potential as a near-point-of-care tool for LTBI screening in resource-constrained settings.