Interferon-Gamma Release Assay or Tuberculin Skin Test for diagnosis of latent tuberculosis: An analysis and reconciliation of concordant and discordant results among adults in southern Nigeria
The introduction of interferon-γ (IFNγ) release assays is expected to ameliorate the limitations of the tuberculin skin test (TST) although its high cost and requirements for resource-limited settings such as Nigeria made TST to remain the preferred method for the diagnosis of LTBI. This study used TST and QFT-GIT to test for LTBI in adult voluntary participants in Nigeria. A total of 113 out of 320 test participants tested positive for LTBI (35.3%). The median induration for all ages was 12mm although it was significantly higher among participants over 55 years. The age group also had the highest number of positives accounting for 45%. 31% of participants that tested positive for QFT-GIT were adults above 55 years. The highest number of negatives were recorded among participants aged 18–55 years (12%). In 106 participants, there was substantial agreement and fair concordance between QFT-GIT and TST (κ = 0.32, SE 0.07). Using a cutoff of less than 10mm for a positive TST closed the discordance in negative results while increasing the induration diameter to 15mm for TST resolved the discordance in positive TST. Results showed age was a statistically significant factor to consider when choosing the method of investigation.
1 Cell Biology and Genetics Unit, Department of Zoology, Faculty of Science, University of Ibadan, Ibadan, Nigeria
2 Department of Medical Laboratory Science, School of Public and Allied Health, Babcock University, Ilishan-Remo, Ogun state, Nigeria
3 Faculty of Veterinary Medicine, University of Ibadan, Ibadan, Nigeria
4 Department of Community Medicine, Faculty of Public Health, College of Medicine, University of Ibadan, Ibadan, Nigeria