More from
Madhukar Pai. Here he discusses reproducibility
Serial IGRA testing shows that IGRAs are highly dynamic, with high rates of conversions and reversions. Although some of the dynamic changes may be due to test reproducibility some of the kinetics might signal the underlying transitions that occur in the TB spectrum.
For example, rapid reversion of a positive IGRA after exposure is well documented and could imply that infection was eliminated in association with transient T cell priming.
All sorts of theories are challenged - perhaps
one third of the world isn't infected with TB and perhaps there is greater progression to active from those who remain infected.
Some individuals convert their IGRA result from negative to positive and then revert again. Others convert their IGRA result and stay converted, at least in the short term. Certain individuals are repeatedly IGRA-positive for a long time, and others remain IGRA-negative for years, despite ongoing TB exposure. Although no data exist to link these trajectories of test results with disease progression, it is inconceivable that all of these phenotypes will have the same prognosis.
Reversions and conversions can cause heartburn to some diagnosticians - the skin test was so easy!
Those with a transiently positive IGRA result (‘unstable conversions’) may have a low likelihood of disease progression, possibly similar to the persistently negative group. Without serial testing, the underlying phenotypes are not separable, and this will undermine the predictive value of a single test result.
However, without large amounts of data made available progress towards eliminating TB will be limited if not stalled.
Without more predictive biomarkers or combinations of biomarkers, or novel serial testing strategies, we may not be able to translate biological advances into clinical interventions that can eliminate TB.
