Guidelines

Many countries have developed guidelines which incorporate the use of interferon gamma release assays (IGRAs) such as              T-SPOT.TB. The information below is provided as an abbreviated guide to these guidelines. However, we recommend you read the guidelines appropriate for your country.

On 22 March 2006, The National Institute for Health and Clinical Excellence (NICE) published their Guidelines for TB control in England and Wales. They are available online at www.nice.org.uk and are titled ‘Tuberculosis: clinical diagnosis and management of tuberculosis, and measures for its prevention and control'.

The NICE Guidelines recommend:

• Use IGRAs as the front line test for latent TB infection in preference to the tuberculin skin test (TST) where the skin test may be "less reliable" including all immunocompromised patients
• Use IGRAs as a secondary, confirmatory test in all cases when the TST is positive.  The IGRA is used as a means of screening out TST false positives
• IGRAs also have a role to play in the diagnosis of TB disease especially in non-pulmonary TB and as a rule-out test in TB suspects

In October 2007, The Health Protection Agency published a position statement on the use of IGRA tests for TB, providing an update on the NICE guidelines. It is available online at www.hpa.org.uk and is titled ‘Health Protection Agency Position Statement on the use of Interferon Gamma Assay (IGRA) test for Tuberculosis (TB)'.

The main points are:

Active disease
IGRAs may be used when it has not been possible to confirm a diagnosis by culture and when radiological and histopathological evidence is lacking.

Latent Infection
In LTBI IGRAs are at least as sensitive at the TST and in BCG vaccinated populations are more specific. TST should be carried out first and those that are positive should be considered for IGRA testing if available. This would also apply to new entrant screening.

IGRAs should be the only test used in the following situations:

• Where TST may be falsely negative due to immunosuppression
• When screening a large number of people as part of a public health investigations since repeated visits would be impractical

Health care worker screening
New health care workers should be tested with IGRAs as they may come into contact with immunosuppressed patients and because of the logistical simplicity of the tests.

Pre-TNF alpha screening
IGRAs may be a suitable alternative in BCG vaccinated subjects.

If your laboratory is in the UK and is not yet able to provide a blood test, then send your samples to Oxford Immunotec to be run in our T-SPOT.Service.

Click here for more information

In November 2005 the Swiss Lung Association released recommendations for the diagnosis of TB infection in contact investigations using blood tests in Bulletin 45/10 of the Office Federal de la Sante Publique. The main points are: 

• Confirm a positive Mantoux tests with an IGRA
• Use only an IGRA in immunocompromised subjects
• Children are excluded from being tested with IGRAs

In December 2007 the following guidelines were released for the use of IGRAs to screen patients prior to administration of anti-TNF alpha therapies.  

• All patients should be screened for LTBI before being given anti-TNF alpha therapies
• Screening should be based on history, chest x-ray and IGRA (TST is no longer recommended)
• Preventive treatment should be given where LTBI is suspected as a result of:
  • Positive IGRA
  • Abnormal x-ray suggesting TB which was not adequately treated
  • History of significant prior exposure

Recommendations for the identification of LTBI were released jointly by the Associazione di Microbiologia Clinica Italiana (AMCLI) and the Federazione Italiana per le Malattie Polmonari Sociali e la Tubercolosi (FIMPST) in May 2006. The main points are: 

• Mantoux testing should be carried out and where positive an IGRA should be performed
• In subjects with an expected TST positivity rate of 40% or more, and in immunosuppressed patients an IGRA should be carried out without a prior TST
• IGRAs may be used along with other tests in the diagnosis of active disease

Dutch guidelines for contact tracing and screening were released in February 2008. The main points are: 

• Carry out a Mantoux test and where the subsequant induration is more than 5mm perform an IGRA.
• In subjects where the Mantoux “may be less reliable” perform an IGRA without a prior Mantoux.
• IGRAs can be used in place of a Mantoux in the work up for active disease diagnosis

The Haute Autorite de Sante issued preliminary guidelines in December 2006 suggesting that IGRA tests should be used in the following settings: 

• Contact tracing in subjects older than 15 years
• Health care workers where a TST may not be reliable
• To assist in the diagnosis of active disease, particularly non-pulmonary
• Pre-TNF alpha therapy screening

Draft guidelines published in July 2008 proposed that IGRAs can be used in the following settings: 

• Contact tracing (in conjunction with a TST)
• In certain circumstances IGRAs, if available can be considered as the sole test for LTBI:
  • Where the TST may be falsely negative due to immunosuppression
  • When screening large numbers of individuals as part of a public health investigation
• Pre-employment screening of healthcare workers
• For individuals, commencing immunosuppressive therapy e.g. TNF-α antagonists