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A novel, portable assay can deliver TB diagnoses in under an hour at low cost using samples of blood, saliva, or sputum, according to a recent study.

Researchers have engineered a portable “lab‑in‑tube” (LIT) assay that detects Mycobacterium tuberculosis (Mtb) DNA directly from blood, saliva, or sputum in less than 60 minutes at a relatively low cost, according to a study published in Science Translational Medicine.

“Over 90% of TB [tuberculosis] cases occur in low- and middle-income countries. An estimated 4.2 million TB cases were undiagnosed or unreported in 2021, largely because of limitations and costs of microbiological and molecular-based TB testing in areas with high disease burden given that these tests require expertise, equipment, and infrastructure that are not available in resource-limited settings,” wrote study author Tony Ye Hu, PhD, of Tulane University, and colleagues. “Rapid portable assays are needed to improve diagnosis, treatment, and reduce transmission of tuberculosis (TB), but current tests are not suitable for patients in resource-limited settings with high TB burden.”

Portable, Rapid, Low-Cost Testing

According to the authors, the LIT system comprises a microprocessor-controlled device that utilizes an LCD user interface to control assay performance, automate assay analysis, and display results in a simple readout. The single-tube assay uses a DNA enrichment membrane and a low-cost cellulose disc containing lyophilized recombinase polymerase amplification and CRISPR-Cas12a (a type V CRISPR-associated protein used for genome editing and nucleic acid detection) reagents, which achieve single-nucleotide specificity and high sensitivity within 1 hour of sample application, eliminating the need for a conventional DNA isolation procedure.

The LIT system provides a low-cost solution for TB detection, with an estimated cost of under $800 for the device and individual tests costing less than $3, the researchers stated. In comparison, another commonly used TB device costs a minimum of $19,000, with an approximate cost of $8 per sample.

Robust Performance

The research team tested the system’s performance using cell-free DNA isolated from sera of a pediatric cohort with pulmonary and extrapulmonary TB. The LIT device demonstrated high sensitivity compared to culture and GeneXpert MTB/RIF results (81% vs 55% and 68%), meeting the WHO target product profile criteria for new nonsputum TB diagnostics.

“Changes in assay results for serum isolated during treatment were also highly predictive of clinical response,” the authors noted.

Findings showed that results obtained using noninvasive sputum and saliva specimens from adults with bacteriologically confirmed pulmonary TB were also comparable to those reported for reference methods, suggesting that both respiratory and serum/plasma specimens may have value in improving TB screening.

“This rapid and inexpensive lab-in-tube assay approach thus represents one means to address the need for point-of-care TB diagnostics useable in low-resource settings,” the authors concluded.