Evaluation of the High Indeterminate Rate of the QuantiFERON®-Tb Gold In-Tube Assay in a Children’s Hospital

Abstract

BackgroundThe QuantiFERON®-Tb Gold In-Tube (QFT) assay is an in vitro diagnostic test for Mycobacterium tuberculosisinfection. We observed a high indeterminate rate among inpatients at Steven and Alexandra Cohen Children’s Medical Center of New York. We hypothesized this was caused by incorrect specimen collection. We educated healthcare workers in proper collection techniques and studied the effect on the indeterminate rate.MethodsWe recorded the results of the QFT test for pediatric inpatients from November 2012 to December 2016 from a laboratory specimen log. Beginning in April 2015, multimode education was implemented using an instructional card that accompanied the QFT tubes, presentations, and an instructional video. We used an electronic survey to assess knowledge of healthcare workers before and after the education intervention. We abstracted demographic, clinical, and laboratory factors to analyze correlation with the indeterminate rate.ResultsThere were 216 subjects, 101 during the pre-education period and 115 during the post-education period. Ninety-three (43.1%) were indeterminate, 8 (3.7%) were positive, and 115 (53.2%) were negative. There was no significant difference in indeterminate result rate between pre and post-education groups, 46% and 40%, respectively (P = 0.33). In a multivariable model of factors associated with an indeterminate result, there was no significant association with education (P = 0.86), immunocompromised status (P = 0.6009), or comorbidities (P = 0.15). Age (P = 0.0007), absolute lymphocyte count (ALC) (P = 0.0016), and recent receipt of immunosuppressive medication (IS) (P = 0.0001) were significantly associated with an indeterminate result. Among those surveyed after the education period there was a significantly higher proportion of persons who received training (P < 0.0001), reported shaking the tubes after blood inoculation (P < 0.0001), and reported using a waste tube before collection (P < 0.0001) compared those surveyed prior to the education period.ConclusionAlthough education resulted in an increase in knowledge of correct specimen collection, the indeterminate rate remained high. Younger patient age, recent receipt of IS, and lower ALC are factors associated with an indeterminate result.Disclosures All authors: No reported disclosures.