Ultrasensitive urine test spots TB biomarkers, aids HIV-positive diagnosis

Tuberculosis (TB) remains one of the leading causes of death worldwide despite being curable using antibiotics. A stark problem is that most people who die of TB never begin treatment, in large part because available diagnostics are not sensitive enough or are not accessible to many patients. To tackle that gap, a team led by corresponding author David R. Walt set out to detect very low levels of TB-related molecules in urine, rather than relying on samples that can be harder to collect or analyze. The researchers developed and validated an ultrasensitive multiplex Single Molecule Array (Simoa) assay designed to find trace amounts of TB biomarkers in safe-to-use, accessible urine samples. By focusing on urine and on tools capable of measuring single molecules, the group aimed to create a test that could pick up infections earlier or in people for whom standard tests fail. Their work tests whether measuring these low-abundance signals can help clinicians decide when to start treatment and reduce the number of people who never receive care.

The new assay measures two TB biomarkers: lipoarabinomannan (LAM) and antigen 85B (Ag85B). The team used antibodies that recognize different parts, or epitopes, of LAM in a four-plex assay made up of three LAM antibody pairs and one Ag85B antibody pair. They trained a diagnostic model on measured signals and then demonstrated its performance in retrospective cohorts totaling 576 individuals from South Africa, Peru, Vietnam, and Cambodia. The study included a blinded test cohort of 215 samples to assess real-world accuracy. Overall, the assay classified samples with 98% specificity and 45% sensitivity, meaning it had a low false-positive rate but detected less than half of true cases across the whole group. Importantly, sensitivity rose to 58% among people living with the human immunodeficiency virus (HIV). The researchers also report that LAM concentrations measured in urine depend on the antibodies used to measure them, and that this Simoa approach is more sensitive than the existing AlereLAM lateral flow test for TB in HIV-positive individuals.

These findings suggest a promising direction: an ultrasensitive, urine-based test could serve as an adjunctive tool to help clinicians start TB treatment, especially in people living with HIV. Because the assay uses urine, it relies on a sample type that is easy and safe to collect, which could improve access in many settings. The higher sensitivity in HIV-positive individuals indicates this approach may fill a current gap where some existing tests underperform. At the same time, an overall sensitivity of 45% shows the test is not yet a standalone diagnostic for all patients, and the dependence of measured LAM concentrations on the specific antibodies used highlights how critical assay design is for performance. The authors frame this work as a first step toward an adjunctive diagnostic test: a tool that could be used alongside other clinical information and tests to reduce missed diagnoses and get more people onto lifesaving antibiotics sooner.