A UK study has shown potential for a new blood test to diagnose human tuberculosis (TB) and identify those most at risk of developing the disease.

Researchers found the Actiphage assay, which has been commercialised by PBD Biotech for the livestock industry as a blood or milk test for bovine TB and Johne’s disease, was able to positively identify human TB with 73% accuracy.

The 66 participants in the study were divided into four groups: those with active pulmonary TB, those with latent TB, a control group of patients referred for suspected TB but found not to have the disease and a control group of healthy individuals.

Around a quarter of the world’s population carry the latent form of TB, which has no symptoms and cannot be passed on to other people. About 10% of people with latent TB will go on to develop an active form of the disease, the mechanism behind which is understood to be linked to immune system changes.

Current TB diagnostics are all based on sputum samples coughed up from the lungs, but some patients – particularly children – can find producing sputum difficult. These tests can also be problematic when diagnosing cases of extrapulmonary TB where the disease has spread outside of the lungs, which is particularly common in HIV patients with a prior latent infection whose immune system has failed.

PBD Biotech director of R&D Dr Ben Swift said: “A blood test is an easy sample to take and process and it gives you a lot of information. If we can detect viable bacteria in the Actiphage test we can say that this individual is definitely infected with a live bug. We see it as quite a powerful tool in addition to what doctors do to confirm the diagnosis of TB and look to monitor treatment in the future.”

The patients underwent Actiphage testing twice, 12 months apart, with Actiphage testing positively in 73% of people who were subsequently diagnosed with TB. Three of the participants with latent TB infection tested positive on Actiphage, two of whom went on to develop the disease more than six months later. This suggests the test may be able to identify people with latent TB who are at risk of developing active TB.

The assay also had strong specificity, with none of the patients in the control groups testing positive and none of the patients with latent TB who tested negative going on to develop active TB.

PBD Biotech chief scientific officer Dr Catherine Rees said: “While we are cautious about generalising from a small sample size, we are optimistic that these initial findings indicate that Actiphage can be used as a tool to help us better understand the dynamics of the infection in humans.”