Serial interferon-gamma release assay (IGRA) testing to monitor treatment responses in cases of feline mycobacteriosis

The interferon-gamma release assay (IGRA) is used to diagnose cases of feline myco-bacteriosis, but the use of serial testing to monitor treatment responses has not been evaluated in this species. From a population of cats that underwent IGRA testing for diagnostic investiga-tion, individuals were identified with a pre- and end of treatment IGRA that passed control thresholds. The number of cats who reverted to negative at the end of treatment IGRA, changes in paired antigen-specific optical density (OD) values and differences in the pre-treatment anti-gen-specific OD values for those who underwent reversion were compared. Factors to explain reversion or recurrence of disease post-treatment were explored. Four of 18 cats (22%) reverted to negativity at the point of clinical resolution (p = 0.33), there was no difference in paired anti-gen-specific OD values (p ≥ 0.12), and cats that reverted did not have a lower baseline OD value (p = 0.63). No statistically significant factors were identified to predict reversion (p ≥ 0.08). Re-maining positive at the end of treatment IGRA was not associated with recurrence of disease post-treatment (p = 0.34). Overall, these data suggest there is limited value in the use of the IGRA to monitor treatment responses in cats.