Novel blood tests for TB could accelerate diagnosis

Rapid blood tests currently in use are unable to rule out tuberculosis and should be replaced with a more accurate test, according to a UK study published in The Lancet journal.

In the largest study to date of rapid TB tests used by UK's National Health Service (NHS), a team led by researchers at Imperial College London found that available tests are not sensitive enough to rule out a diagnosis of TB in suspected cases, and so have limited clinical use.

The research, published in the journal Lancet Infectious Diseases, also looked at a new second generation rapid blood test, developed at Imperial, and found it to be substantially more accurate than the existing tests.

According to the team, once implemented the new test could enable doctors to quickly detect or rule out TB infection and help them to distinguish patients who need further investigation and treatment from those who do not and pose no infectious risk to others.

"Tests of thousands of patients undergo diagnostic assessment for symptoms suggestive of TB, resulting in over 5,000 cases of TB diagnosed each year," said Ajit Lalvani, Chair in infectious Diseases at the National Heart and Lung Institute at Imperial College London.

"Stopping the use of the existing, inadequate tests could save the NHS a lot of money. In contrast, the new, more accurate rapid blood test, will improve and accelerate diagnostic assessment of patients with suspected TB," said Lalvani, who led the study.

TB is a bacterial infection affecting the lungs, causing cough, weight loss and fevers, and is spread through droplets from coughs and sneezes from infected patients.

Diagnosing and treating the condition early is essential for the health of the patient as well as for preventing the spread of TB to others. There is therefore a need for rapid, convenient tests to rule out a TB diagnosis in s suspected cases based on a blood sample.

Currently available rapid tests for TB used by the NHS, known as interferon-gamma release-assays (IGRAs) can help to indicate if a patient has TB infection by detecting their immune response to TB bacteria based on a blood sample.

In the latest study, researchers compared existing commercially available IGRA tests against new generation tests in 845 patients with suspected TB in 10 NHS hospitals in England.

Patient blood samples were analysed using both sets of tests, the result of which benchmarked against a confirmed diagnoses based on positive culture results.

Analysis of the rapid test results revealed that the second-generation test has a diagnostic sensitivity of 94 per cent in patients with confirmed TB -- meaning it gives a positive result for 94 per cent of patients with infection -- significantly and substantially higher than either of the existing commercially available IGRA tests (which range from 67.3 per cent and 81.4 per cent).

The findings indicate the test would be much more accurate at ruling out TB infection in suspected cases of TB, so saving time and resources and enabling patients to receive treatment more rapidly.