Background The QuantiFERON？-TB Gold In-Tube test (QFT-GIT) is a viable alternative to the tuberculin skin test (TST) for detecting Mycobacterium tuberculosis infection. However, within-subject variability may limit test utility. To assess variability, we compared results from the same subjects when QFT-GIT enzyme-linked immunosorbent assays (ELISAs) were performed in different laboratories. Methods Subjects were recruited at two sites and blood was tested in three labs. Two labs used the same type of automated ELISA workstation, 8-point calibration curves, and electronic data transfer. The third lab used a different automated ELISA workstation, 4-point calibration curves, and manual data entry. Variability was assessed by interpretation agreement and comparison of interferon-γ (IFN-γ) measurements. Data for subjects with discordant interpretations or discrepancies in TB Response >0.05 IU/mL were verified or corrected, and variability was reassessed using a reconciled dataset. Results Ninety-seven subjects had results from three labs. Eleven (11.3%) had discordant interpretations and 72 (74.2%) had discrepancies >0.05 IU/mL using unreconciled results. After correction of manual data entry errors for 9 subjects, and exclusion of 6 subjects due to methodological errors, 7 (7.7%) subjects were discordant. Of these, 6 (85.7%) had all TB Responses within 0.25 IU/mL of the manufacturer's recommended cutoff. Non-uniform error of measurement was observed, with greater variation in higher IFN-γ measurements. Within-subject standard deviation for TB Response was as high as 0.16 IU/mL, and limits of agreement ranged from ？0.46 to 0.43 IU/mL for subjects with mean TB Response within 0.25 IU/mL of the cutoff. Conclusion Greater interlaboratory variability was associated with manual data entry and higher IFN-γ measurements. Manual data entry should be avoided. Because variability in measuring TB Response may affect interpretation, especially near the cutoff, consideration should be given to developing a range of values near the cutoff to be interpreted as “borderline,” rather than negative or positive.
References
[1]
Denkinger CM, Dheda K, Pai M (2011) Guidelines on interferon-gamma release assays for tuberculosis infection: concordance, discordance or confusion? Clin Microbiol Infect 17: 806–814.
[2]
Mazurek GH, Jereb J, Vernon A, LoBue P, Goldberg S, et al. (2010) Updated guidelines for using Interferon Gamma Release Assays to detect Mycobacterium tuberculosis infection - United States, 2010. MMWR Recomm Rep 59: 1–25.
[3]
Pai M, Zwerling A, Menzies D (2008) Systematic review: T-cell-based assays for the diagnosis of latent tuberculosis infection: an update. Ann Intern Med 149: 177–184.
[4]
Diel R, Goletti D, Ferrara G, Bothamley G, Cirillo D, et al. (2010) Interferon-{gamma} release assays for the diagnosis of latent M. tuberculosis infection: A systematic review and meta-analysis. Eur Respir J 37: 88–99.
[5]
Ewer K, Millington KA, Deeks JJ, Alvarez L, Bryant G, et al. (2006) Dynamic antigen-specific T-cell responses after point-source exposure to Mycobacterium tuberculosis. Am J Respir Crit Care Med 174: 831–839.
[6]
Katiyar SK, Sampath A, Bihari S, Mamtani M, Kulkarni H (2008) Use of the QuantiFERON-TB Gold In-Tube test to monitor treatment efficacy in active pulmonary tuberculosis. Int J Tuberc Lung Dis 12: 1146–1152.
[7]
Pai M, Joshi R, Dogra S, Mendiratta DK, Narang P, et al. (2006) Persistently elevated T cell interferon-gamma responses after treatment for latent tuberculosis infection among health care workers in India: a preliminary report. J Occup Med Toxicol 1: 7.
[8]
Pollock NR, Kashino SS, Napolitano DR, Sloutsky A, Joshi S, et al. (2009) Evaluation of the effect of treatment of latent tuberculosis infection on QuantiFERON-TB gold assay results. Infect Control Hosp Epidemiol 30: 392–395.
[9]
Ribeiro S, Dooley K, Hackman J, Loredo C, Efron A, et al. (2009) T-SPOT.TB responses during treatment of pulmonary tuberculosis. BMC Infect Dis 9: 23.
[10]
Baker CA, Thomas W, Stauffer WM, Peterson PK, Tsukayama DT (2009) Serial testing of refugees for latent tuberculosis using the QuantiFERON-gold in-tube: effects of an antecedent tuberculin skin test. Am J Trop Med Hyg 80: 628–633.
[11]
Belknap R, Kelaher J, Wall K, Daley C, Schluger N, et al. (2009) Diagnosis of Latent Tuberculosis Infection in U.S. Health Care Workers: Reproducibility, Repeatability and 6 Month Follow-Up with Interferon-gamma Release Assays (IGRAs). American Journal of Respiratory and Critical Care Medicine 179: A4101.
[12]
Costa JT, Silva R, Sa R, Cardoso MJ, Ribeiro C, et al. (2010) Comparison of interferon-gamma release assay and tuberculin test for screening in healthcare workers. Rev Port Pneumol 16: 211–221.
[13]
Detjen AK, Loebenberg L, Grewal HM, Stanley K, Gutschmidt A, et al. (2009) Short-term reproducibility of a commercial interferon gamma release assay. Clin Vaccine Immunol 16: 1170–1175.
[14]
Pai M, Joshi R, Dogra S, Mendiratta DK, Narang P, et al. (2006) Serial testing of health care workers for tuberculosis using interferon-gamma assay. Am J Respir Crit Care Med 174: 349–355.
[15]
Perry S, Sanchez L, Yang S, Agarwal Z, Hurst P, et al. (2008) Reproducibility of QuantiFERON-TB gold in-tube assay. Clin Vaccine Immunol 15: 425–432.
[16]
Pollock NR, Campos-Neto A, Kashino S, Napolitano D, Behar SM, et al. (2008) Discordant QuantiFERON-TB Gold test results among US healthcare workers with increased risk of latent tuberculosis infection: a problem or solution? Infect Control Hosp Epidemiol 29: 878–886.
[17]
Ringshausen FC, Nienhaus A, Schablon A, Schlosser S, Schultze-Werninghaus G, et al. (2010) Predictors of persistently positive Mycobacterium-tuberculosis-specific interferon-gamma responses in the serial testing of health care workers. BMC Infect Dis 10: 220.
[18]
Ringshausen FC, Nienhaus A, Torres CJ, Knoop H, Schlosser S, et al. (2011) Within-subject Variability of Mycobacterium-tuberculosis-specific Interferon-gamma Responses in German Health Care Workers. Clin Vaccine Immunol 18: 1176–1182.
[19]
van Zyl-Smit RN, Pai M, Peprah K, Meldau R, Kieck J, et al. (2009) Within-subject Variability and Boosting of T Cell IFN-{gamma} Responses Following Tuberculin Skin Testing. Am J Respir Crit Care Med 180: 49–58.
[20]
Veerapathran A, Joshi R, Goswami K, Dogra S, Moodie EE, et al. (2008) T-cell assays for tuberculosis infection: deriving cut-offs for conversions using reproducibility data. PLoS ONE 3: e1850.
[21]
Zwerling A, Cloutier-Ladurantaye J, Pietrangelo F, Behr M, Schwartzman K, et al. (2009) Conversions and Reversions in Health Care Workers in Montreal, Canada Using QuantiFERON-TB-Gold In-Tube. Am J Respir Crit Care Med 179: A1012.
[22]
Doberne D, Gaur RL, Banaei N (2011) Preanalytical delay reduces sensitivity of QuantiFERON-TB Gold In-Tube for detection of latent tuberculosis infection. Journal of Clinical Microbiology 49: 3061–3064.
[23]
Park JS, Lee JS, Kim MY, Lee CH, Yoon HI, et al. (2012) Monthly follow-ups of interferon gamma release assays among healthcare workers in contact with TB patients. Chest doi:10.1378/chest.11-3299.
[24]
Zwerling A, van den HS, Scholten J, Cobelens F, Menzies D, et al. (2011) Interferon-gamma release assays for tuberculosis screening of healthcare workers: a systematic review. Thorax 67: 62–70.
Powell RD III, Whitworth WC, Bernardo J, Moonan PK, Mazurek GH (2011) Unusual Interferon Gamma Measurements with QuantiFERON-TB Gold and QuantiFERON-TB Gold In-Tube Tests. PLoS ONE 6: e20061.
[27]
Beckerman H, Roebroeck ME, Lankhorst GJ, Becher JG, Bezemer PD, et al. (2001) Smallest real difference, a link between reproducibility and responsiveness. Qual Life Res 10: 571–578.
[28]
Guyatt GH, Kirshner B, Jaeschke R (1992) Measuring health status: what are the necessary measurement properties? J Clin Epidemiol 45: 1341–1345.
[29]
Hopkins WG (2000) Measures of reliability in sports medicine and science. Sports Med 30: 1–15.
[30]
Atkinson G, Nevill A (2000) Typical error versus limits of agreement. Sports Med 30: 375–377.
[31]
Bland JM, Altman DG (1986) Statistical methods for assessing agreement between two methods of clinical measurement. Lancet 1: 307–310.
[32]
Lu L, Shara N (2007 November) Reliability analysis: Calculate and Compare Intra-class Correlation Coefficients (ICC) in SAS. Northeast SAS User's Group Website, 2007 Conference Proceedings. Available: http://www.nesug.org/proceedings/nesug07？/sa/sa13.pdf. Accessed 2012 Aug 15.
[33]
Bland JM (2006 October) How should I calculate a within-subject coefficient of variation? Martin Bland website. Available: http://www-users.york.ac.uk/~mb55/meas/c？v.htm. Accessed 2012 Aug 15.
[34]
Pai M, Joshi R, Dogra S, Zwerling AA, Gajalakshmi D, et al. (2009) T-cell assay conversions and reversions among household contacts of tuberculosis patients in rural India. Int J Tuberc Lung Dis 13: 84–92.
