PURPOSE:
Tuberculosis is relatively uncommon in Australia however 10 million individuals fall ill to TB and 1.4 million deaths annually attributed to TB. It is estimated that a quarter of the world’s population is infected with TB with either active or latent TB.
Originally the tuberculin skin test was utilised for the diagnosis of latent TB infection and more recently the QuantiFERON-TB gold plus test was adopted across Australia as the test of choice. A new assay the TB-IGRA test has been released into the Australian market and has been evaluated at the Royal Hobart Hospital over a period of 6 months against the QuantiFERON-TB gold assay, acknowledging there is no gold standard testing process.
RESULTS:
A total of 455 patient samples were tested with 89.9% concordance between the two assays. Of the 46 discordant results 52.2% were negative on QuantiFERON-TB Gold plus whilst positive on the VIDAS TB-IGRA assay, 17.4% were positive on the QuantiFERON-TB Gold plus and negative on the VIDAS TB-IGRA assay and the remaining 30.4% were indeterminate on QuantiFERON-TB Gold plus with either a positive or negative result on the TB-IGRA assay.
CONCLUSION:
Overall, the evaluation of the TB-IGRA assay provided less indeterminate results versus the QuantiFERON-TB Gold plus assay, which would result in a decrease in the number of patients recalled for retesting and both test methods had good concordance.
The TB-IGRA assay utilises a single lithium heparin tube versus the pack of four tubes required for the QuantiFERON-TB Gold plus assay. The TB-IGRA is a totally automated assay which performs pipetting, incubation and interpretation on board the VIDAS 3 instrument.
For laboratories with smaller numbers of requests for QuantiFERON/IGRA testing the TB-IGRA test is a viable alternative.