title: Comparison of QuantiFERON-TB Gold test and tuberculin skin test for the identification of latent Mycobacterium tuberculosis infection in lupus patients.
abstract: The tuberculin skin test (TST) has low sensitivity for the diagnosis of tuberculosis (TB). QuantiFERON-TB Gold (QFT-G) is an IFN-gamma-release assay that measures the release of interferon-gamma after stimulation in vitro by Mycobacterium tuberculosis antigens using ELISA. The main advantage of this assay compared with TST is the lack of cross-reaction with Bacillus Calmette-Guérin (BCG) as well as most of non-tuberculous mycobacteria. The aim of our study is to compare QFT-G with TST for the detection of latent tuberculosis infection (LTBI) among patients with systemic lupus erythematosus (SLE).
  
  
  METHODS
  Seventy-eight patients with SLE and 49 healthy subjects (HCs) participated in the study. All patients and controls were interviewed for a history of TB then BCG vaccinations were recorded and chest X-rays were examined for a sign of TB infection. QTF-G and TST were performed on both patients and controls. QTF-G results were recorded as positive, negative or indeterminate. A positive TST for SLE was defined as ≥5 mm.
  
  
  RESULTS
  Seventy-six SLE patients (97.4%) had been BCG vaccinated. Similar to the HC (28.5%), 19 of 78 (24.3%) SLE patients had positive QTF-G. Two patients had an indeterminate result. The agreement between QTF-G and TST was 49/76 (64.4%) (κ = 0.33). There were fewer positive QFT-G test results than positive TST results (24.3% vs. 50%; p < 0.01). Twenty-two (28.9%) patients were TST(+)/QTF-G(-) while only 3(3.9%) patients were TST(-)/QTF-G(+). When the positive TST was defined as ≥10 mm indurations, which is the cut-off in screening for LTBI in Turkey, the agreement between two tests increased up to 58/76 (76.3%) with a κ value of 0.47. The mean TST measurements was higher in QTF-G positive patients (13.4 ± 8.8 mm) than the QTF-G negative patients (4 ± 5.3 mm) (p < 0.001).
  
  
  CONCLUSIONS
  In a TB-endemic and BCG vaccinated population, the QuantiFERON-TB Gold assay seemed to be a more accurate test for the detection of LTBI in SLE patients. Although 5 mm is usually accepted to be the standard cut-off for TST in immunocompromised patients such as SLE, the level of agreement between QTF-G and TST was better with a 10 mm cut-off in our population.
authors.affiliation: Rheumatology, Marmara University Faculty of Medicine, Turkey. dr.yilmazneslihan@gmail.com
authors.forename: N
authors.initials: N
authors.lastname: Yilmaz
authors.forename: S
authors.initials: S
authors.lastname: Zehra Aydin
authors.forename: N
authors.initials: N
authors.lastname: Inanc
authors.forename: S
authors.initials: S
authors.lastname: Karakurt
authors.forename: H
authors.initials: H
authors.lastname: Direskeneli
authors.forename: S
authors.initials: S
authors.lastname: Yavuz
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D001500:BCG Vaccine / Q000008:administration & dosage; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D059425:Interferon-gamma Release Tests / Q000379:methods*; D055985:Latent Tuberculosis / Q000175:diagnosis*; D008180:Lupus Erythematosus, Systemic / Q000150:complications* / Q000276:immunology; D008297:Male; D008875:Middle Aged; D009169:Mycobacterium tuberculosis / Q000302:isolation & purification; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014374:Tuberculin Test / Q000379:methods*; D055815:Young Adult
chemical_list: D001500:BCG Vaccine