title: Thermostability of IFN-γ and IP-10 release assays for latent infection with Mycobacterium tuberculosis: A TBnet study.
abstract: Interferon-γ (IFN-γ) inducible protein 10kD (IP-10) and IFN-γ release assays (IGRAs) are immunodiagnostic tests aiming to identify the presence of specific cellular immune responses, interpreted as markers for latent infection with Mycobacterium tuberculosis. Incubation at higher temperatures could affect IFN-γ and IP-10 responsiveness in order to improve the performance of IP-10 release assays and IGRAs.
  
  
  
  The aim of this study was to assess the robustness of whole blood based IP-10 release assay and IGRAs and the effect of hyper-thermic incubation (39 °C) on the diagnostic accuracy of IP-10 release assay and IGRAs.
  
  
  
  We included 65 patients with confirmed pulmonary tuberculosis and 160 healthy controls from 6 European centres collaborating in the TBnet. In patients, IP-10 responses increased 1.07 (IQR 0.90-1.36) fold and IFN-γ responses decreased 0.88 (IQR 0.57-1.02) fold, with 39 °C compared to 37 °C incubation temperature. At 37 °C IGRA sensitivity was 85% and IP-10 sensitivity was 82%, whereas specificity was 97% for both tests (p > 0.8). These minor changes observed as a result of hyper-thermic incubation were not sufficient to impact IGRA and IP-10 release assay test performance.
  
  
  
  The performance of IGRA and IP-10 release assays is robust despite variations in the incubation temperature between 37 °C and 39 °C.
authors.affiliation: Department of Infectious Disease Immunology, Statens Serum Institut, Copenhagen, Denmark.
authors.forename: Thomas
authors.initials: T
authors.lastname: Blauenfeldt
authors.affiliation: Department of Infectious Diseases and Center for Chronic Immunodeficiency, Medical Center, University of Freiburg, Freiburg, Germany.
authors.forename: Dirk
authors.initials: D
authors.lastname: Wagner
authors.affiliation: Department of Double Diagnosis, Mental Health Centre Sct. Hans, Roskilde, Denmark.
authors.forename: Martine
authors.initials: M
authors.lastname: Aabye
authors.affiliation: Division of Clinical Infectious Diseases, Research Center Borstel, Germany.
authors.forename: Jan
authors.initials: J
authors.lastname: Heyckendorf
authors.affiliation: Department of Infectious Diseases and Center for Chronic Immunodeficiency, Medical Center, University of Freiburg, Freiburg, Germany.
authors.forename: Berit
authors.initials: B
authors.lastname: Lange
authors.affiliation: Division of Clinical Infectious Diseases, Research Center Borstel, Germany; German Center for Infection Research Tuberculosis Unit International Health/Infectious Diseases, University of Lübeck, Germany; Department of Internal Medicine, University of Namibia School of Medicine, Windhoek, Namibia; Department of Medicine, Karolinska Institute, Stockholm, Sweden.
authors.forename: Christoph
authors.initials: C
authors.lastname: Lange
authors.affiliation: Division of Clinical Infectious Diseases, Research Center Borstel, Germany.
authors.forename: Martin
authors.initials: M
authors.lastname: Ernst
authors.affiliation: Department of Pulmonary and Infectious Diseases, Nordsjaelland Hospital, Hillerød, Denmark.
authors.forename: Pernille
authors.initials: P
authors.lastname: Ravn
authors.affiliation: Tuberculosis Outpatient Centre Vila Nova de Gaia, Portugal; Hospital Centre of Vila Nova de Gaia/Espinho, Portugal; Medical School, Porto University, Portugal; Institute of Public Health, Porto University, Portugal.
authors.forename: Raquel
authors.initials: R
authors.lastname: Duarte
authors.affiliation: Pulmonology Diagnostic Center Porto and Vila Nova de Gaia, Portugal.
authors.forename: Clara
authors.initials: C
authors.lastname: Morais
authors.affiliation: Division of Infectious Diseases and Hospital Epidemiology, Cantonal Hospital St.Gallen, Switzerland.
authors.forename: Matthias
authors.initials: M
authors.lastname: Hoffmann
authors.affiliation: Division of Pneumology, Department of Internal Medicine, Cantonal Hospital St.Gallen, Switzerland.
authors.forename: Otto D
authors.initials: OD
authors.lastname: Schoch
authors.affiliation: Servei de Microbiologia, Institut d'Investigació en Ciències de la Salut Germans Trias i Pujol, Universitat Autònoma de Barcelona, Ciber Enfermedades Respiratorias, Instituto de Salud Carlos III, Badalona, Spain.
authors.forename: Jose
authors.initials: J
authors.lastname: Dominguez
authors.affiliation: Servei de Microbiologia, Institut d'Investigació en Ciències de la Salut Germans Trias i Pujol, Universitat Autònoma de Barcelona, Ciber Enfermedades Respiratorias, Instituto de Salud Carlos III, Badalona, Spain.
authors.forename: Irene
authors.initials: I
authors.lastname: Latorre
authors.affiliation: Department of Infectious Disease Immunology, Statens Serum Institut, Copenhagen, Denmark. Electronic address: moru@ssi.dk.
authors.forename: Morten
authors.initials: M
authors.lastname: Ruhwald
mesh_terms: D000328:Adult; D019540:Area Under Curve; D015415:Biomarkers / Q000097:blood; D016022:Case-Control Studies; D054357:Chemokine CXCL10 / Q000097:blood*; D005060:Europe; D005260:Female; D054884:Host-Pathogen Interactions; D006801:Humans; D007371:Interferon-gamma / Q000097:blood*; D059425:Interferon-gamma Release Tests; D055985:Latent Tuberculosis / Q000097:blood / Q000175:diagnosis* / Q000276:immunology; D008297:Male; D008875:Middle Aged; D009169:Mycobacterium tuberculosis / Q000276:immunology* / Q000472:pathogenicity; D011237:Predictive Value of Tests; D011446:Prospective Studies; D055550:Protein Stability; D012372:ROC Curve; D015203:Reproducibility of Results; D013048:Specimen Handling / Q000379:methods*; D013696:Temperature; D014397:Tuberculosis, Pulmonary / Q000097:blood / Q000175:diagnosis* / Q000276:immunology; D055815:Young Adult
chemical_list: D015415:Biomarkers; C114753:CXCL10 protein, human; D054357:Chemokine CXCL10; C573415:IFNG protein, human; D007371:Interferon-gamma
keywords: Hyperthermia; IGRA; IP-10 release assay; Mycobacterium. tuberculosis