Implementing IGRAs in the UK: Constraints and opportunities

The UK has issued IGRA Guidelines by the National Institute for Health and Clinical Excellence (NICE), but the science is changing rapidly. The Health Protection Agency (HPA) has released a position statement to address some of the changes. The crux of the UK guidelines is a two-step testing approach, the basis of which is a cost-effectiveness analysis. All household contacts are investigated, irrespective of the disease site in the index case. The NICE guidelines call for an initial TST followed by an IGRA if the TST is positive (≥15 mm if the person had BCG or ≥5 mm if the person had not received BCG). The IGRA (if available) is then given if the TST is positive. Occasionally, wider screening beyond household contacts is required. Three examples were cited where the IGRA was successfully used for expanded investigations. Regarding TB immigrant screening, NICE recommends screening for latent infection only for those from countries in sub-Saharan Africa or a country with TB incidence >500/100 000. For those aged <16 or 16-35, if they have a chest X-ray that is normal, they are given a TST. A TST is also given to pregnant women. To address the issue of boosting, the HPA position statement now recommends IGRA at time of reading of the TST. There are other IGRA implementation issues, such as when to do the IGRA test following exposure and what should be the role for the test in children. While IGRAs are here to stay, it would be useful if we could develop studies on IGRA cost-effectiveness based on predictive value to help judge the test. The impact of this test is likely to be modest in England because of the low overall incidence.