Fingerstick blood test can be a promising TB screening tool, study finds

A study has found a new fingerstick blood test to be a promising tool for screening tuberculosis patients. But it’s too early to say if it’s the game changer the TB community needs to detect more TB cases and prevent transmission.

The study recruited 195 participants from Gambia, Uganda, South Africa, and Vietnam. Seventy-five of the participants had TB and 120 didn't. The results were based on a test using GeneXpert Ultra — an upgraded version of GeneXpert, a rapid diagnostic tool for TB that uses a sputum sample.

When the fingerstick blood test was evaluated, researchers found it had an overall sensitivity of 91% and specificity of 86%, regardless of HIV status or geographical location. This meets the World Health Organization’s minimum specifications for a TB triage test, which requires at least 90% sensitivity and at least 70% specificity for pulmonary TB.

The test gives results in under one hour using a few drops of blood, and it will help to determine who has a high likelihood of TB, and will, therefore, require further testing.

Sputum, which is a mixture of saliva and mucus coughed up from the respiratory tract, is not an ideal sample type due to biohazard risks and difficulties in production in children and people living with HIV, Jayne Sutherland, head of the TB research group at the Medical Research Council Unit The Gambia and the study’s lead, told Devex.

The study was recently published in the medical journal Clinical Infectious Diseases and presented Tuesday during a press briefing of the 52nd Union World Conference on Lung Health. Sutherland said that the results are interim and that they plan to recruit close to 2,000 participants to further test the technology’s accuracy.

“We wanted to present our interim findings because we thought … we wanted it to get out in the public domain. But yes, there's still a lot of evaluation to go on until we have the final information,” she said.

The world is still missing a lot of TB cases. According to WHO’s latest global TB report, the number of people newly diagnosed for TB fell from 7.1 million in 2019 to 5.8 million in 2020.

A new study published in preprint and presented at Tuesday’s press briefing also challenged long-held beliefs on TB transmission. The study, carried out by researchers from the University of Cape Town in South Africa, suggests that tidal breathing, or inhalation and exhalation while one is at rest, may be contributing more to TB transmission than coughing.

Given that most people who seek medical care are those who usually experience symptoms such as coughing, this means there’s a need for more active TB case finding of people who are not seeking medical care, said Guy Marks, president at The Union. It also means there’s a need to consider TB’s airborne transmission and how to control that more effectively, he added.

More trials needed

While Sutherland said their study’s results showed that the test works well even among people living with HIV and even in different geographic settings, it is unclear if and when this is going to actually be used in countries.

But more trials are needed to see how the test works for people who have other risk factors for TB, as well for people who have both TB and COVID-19.

“So there's a lot more work that needs to be done, and a lot more patients that need to be recruited before [the test] will be able to get regulatory approval,” she said.

But the test — developed by Cepheid and is currently a prototype — “looks very promising” especially when considering its potential to screen people with a high likelihood of TB within a short period of time, she said.

“Otherwise patients will leave the clinic and not return, or … it just takes too long to get the results to them so they're already transmitting to the community. So if we at least know there's a very high likelihood that they have TB, then we can direct them to the correct services,” she said.