Background Identifying clinical and serological associations of Latent tuberculosis infection (LTBI) in lupus may be important in preventing progression to overt TB. This study aimed to assess prevalence of LTBI, its association with clinical and serological parameters in SLE.
Methods This is a single center prospective observational study. SLE patients with no prior TB were recruited (n=219). Demography and disease parameters were noted at baseline, 6 and 12 months. LTBI was assessed using TB-IGRA (IFN-γ release assay) and SLE cases were divided into IGRA positive and negative groups. Correlation of disease activity was assessed with IFN-γ levels in unstimulated tube of TB IGRA (for baseline immune activation).
Results Among 219 patients, prevalence of LTBI was 18.7%. Average disease duration was 3.5 years. Proportion of Ro 52 was higher in IGRA positive (43.9%) than negative group(25.3%) (p=0.014) and anticardiolipin IgM antibody higher in IGRA negative group (12.9%) than positive group (2.4%) (p=0.032). Comparison of clinical features yielded no statistically significant difference. Serology revealed greater proportion of low C4 in IGRA negative as compared to the positive group(p=0.036). There was no correlation of SLE disease activity with the IFN-γ levels in the unstimulated tube of TB IGRA. Follow up data was available for 56% at 1 year and 39% at 6months. There was no significant difference in flares among IGRA positive and negative groups
Conclusions Prevalence of LTBI in SLE cases was 18.7%, much lesser than general population (40%). Higher association of anti-Ro 52 antibody in IGRA positive group along with higher anticardiolipin IgM and low C4 in IGRA negative group were found whose clinical significance is unknown. IFN-γ levels in unstimulated tube of TB IGRA did not correlate with SLE disease activity. IGRA status did not seem to have an impact on disease flares in SLE.
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