diagnosis and screening of latent TB infection

Last reviewed 01/2018

Diagnosing latent TB

• offer Mantoux testing in line with the Green Book to diagnose latent TB in people who are:
  • household contacts (aged 5 years and older) of all people with active TB
  • non-household contacts (other close contacts for example, in workplaces and schools)
• consider interferon-gamma testing for people whose Mantoux testing shows positive results, or in people for whom Mantoux testing may be less reliable, for example BCG-vaccinated people
• if Mantoux testing is inconclusive, refer the person to a TB specialist
• if the Mantoux test is positive (an induration of 5 mm or larger, regardless of BCG history) assess for active TB
• If the Mantoux test is positive but a diagnosis of active TB is excluded, consider an interferon gamma release assay if more evidence of infection is needed to decide on treatment. This could be, for example, if the person needs enhanced case management or if there could be adverse events from treatment
• if the Mantoux is positive, and if an IGRA was done and that is also positive, offer them treatment for latent TB infection

New entrants from high-incidence countries

• offer a Mantoux test to children aged 5-15 years. If positive, follow with an interferon-gamma test
• offer either an interferon-gamma test alone or a dual strategy in people aged 16-35 years. For people aged 35 years or older, consider the individual risks and benefits of likely subsequent treatment, before offering testing. (Refer to other sections for other groups, for example, immunocompromised)
• offer Mantoux testing as the initial diagnostic test for latent TB infection in children younger than 5 years who have recently arrived from a high-incidence country. If the initial test is positive (taking into account the BCG history):
  • refer to a TB specialist to exclude active disease and
  • consider treating latent TB
• if Mantoux testing is unavailable, offer an interferon-gamma release assay

Household contacts aged 2-5 years

• offer Mantoux testing as the initial diagnostic test for latent TB infection in child household contacts between the ages of 2 and 5 years. If the initial test is positive taking into account the BCG history:
  • refer to a TB specialist to exclude active disease and
  • consider treating latent TB
• if the initial Mantoux test is negative but the child is a contact of a person with sputum-smear-positive disease, offer an interferon-gamma test after 6 weeks and repeat the Mantoux test to increase the sensitivity (to reduce false negative results)

Contacts - outbreak situation

• in an outbreak situation when large numbers of people may need to be screened, consider a single interferon-gamma test for people aged 5 years and older

People who are immunocompromised

If latent TB is suspected in children who are immunocompromised, refer to a TB specialist

For adults who are severely immunocompromised, such as those with HIV and CD4 counts of fewer than 200 cells/mm3, or after solid organ or allogeneic stem cell transplant, offer an interferon-gamma release assay and a concurrent Mantoux test.

• if either test is positive (for Mantoux, this is an induration of 5 mm or larger, regardless of BCG history), assess for active TB
• if this assessment is negative, offer them treatment for latent TB infection

For other adults who are immunocompromised, consider an interferon-gamma release assay alone or an interferon-gamma release assay with a concurrent Mantoux test

• if either test is positive (for Mantoux, this is an induration of 5 mm or larger, regardless of BCG history), assess for active TB
• if this assessment is negative, offer them treatment for latent TB infection

Healthcare workers

• offer a Mantoux test to new NHS employees who will be in contact with patients or clinical materials if the employees:
  • are not new entrants from high-incidence countries and
  • have not had BCG vaccination (for example, they are without scar, other documentation or reliable history)
• if the Mantoux test is negative, refer to the Green Book for BCG immunisation guidance. If the Mantoux test is positive, offer an interferon-gamma test
• offer an interferon-gamma test to new NHS employees who have recently arrived from high-incidence countries or who have had contact with patients in settings where TB is highly prevalent
• healthcare workers who are immunocompromised should be screened in the same way as other people who are immunocompromised

Hard-to-reach groups

• Offer people from hard-to-reach groups a single interferon-gamma test

NICE guideline provides guidance based on whether a patient has latent TB (evidence of previous infection and TB is dormant) or have active TB (an ongoing TB related illness such as pulmonary TB)

Reference:

• 1) NICE (March 2011) Tuberculosis: clinical diagnosis and management of tuberculosis, and measures for its prevention and control
• 2) NICE (May 2016). Tuberculosis.