1662. Impact of Blood Volume, Tube Shaking, and Incubation Time on the Reproducibility of QuantiFERON-TB Gold In-Tube Assay
Session: Poster Abstract Session: Mycobacterial Infections
Saturday, October 5, 2013
Room: The Moscone Center: Poster Hall C
  • Poster IDweek - Gaur rl.pdf (734.4 kB)
  • Background: Serial testing studies with interferon gamma release assays (IGRAs) are reporting challenges with reproducibility of results in health care workers (HCWs).  We hypothesized the existence of unrecognized preanalytical sources of variability that contribute to irreproducible results.  In this study we investigated the effect of blood volume (0.8, 1.0, and 1.2 ml), tube shaking (gentle versus vigorous) and duration of incubation (16, 20, and 24 hr) on the QuantiFERON-TB gold in-tube (QFT-GIT) results in 48 (15 infected and 33 uninfected) donors.

    Methods: Blood draw was performed by a trained laboratory phlebotomist and transferred to QFT-GIT tubes by calibrated pipette.  All downstream processes are same for all tubes as per manufacturer instruction. 

    Results: The median TB response (TB Ag - Nil) was significantly higher with 0.8 ml blood (0.87 IU/ml) compared to 1.0 ml (0.84 IU/ml; P = 0.002) and 1.2 ml (0.44 IU/ml; P = 0.0007) in subjects with TB infection.  Compared to 0.8 ml, there was a higher rate of false negative results with 1.0 ml (33.3%; P = 0.15) and 1.2 ml (46.7%; P = 0.02) blood in infected subjects.  Blood volume did not significantly change positivity rates in uninfected controls (P > 0.05).  Compared to gentle shaking, vigorous shaking increased the median IFN-g response in Nil (0.04 vs. 0.05 IU/ml; P = 0.007) and TB Ag (0.06 vs. 0.11 IU/ml; P = 0.05 value) tube but there was no significant change in TB responses (0.01 vs. 0.01, P = 0.7).  Except for TB response at16 hr vs. 24 hr in uninfected donors (P = 0.04), the duration of incubation did not have a significant impact on TB response or the proportion of positive results in uninfected and infected donors (P > 0.05).

    Conclusion: This study identifies blood volume and tube shaking as preanalytical sources of variability which require standardization in order to improve the quality of QFT-GIT results.

    Rajiv Gaur, PhD, Pathology, Stanford University, Palo Alto, CA and Niaz Banaei, MD, Departments of Pathology and Medicine, Division of Infectious Diseases and Geographic Medicine, Stanford University, Palo Alto, CA


    R. Gaur, None

    N. Banaei, None

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