Precision in Practice: Managing Indeterminate TB Testing with Quality Systems

QuantiFERON(R) TB Gold is a test used to diagnose tuberculosis (TB) infection by measuring interferon-gamma release. Test results are reported as:  positive, negative, or indeterminate. The American College of Rheumatology recommends interferon-gamma release assays as the initial test for rheumatoid arthritis patients beginning biological agents. Recently, our laboratory noted an increase in TB tests due to the US Preventive Services Task Force's recommendation for TB testing in high-risk populations for latent TB infection screening. We also observed a rise in indeterminate results, prompting inquiries from providers. In this study, we conducted a retrospective data analysis to investigate indeterminate TB results and identify potential factors contributing to these outcomes.

Methods- The QuantiFERON-TB Gold Plus IFN-γ assay in our laboratory is performed on the Agility (Dynex Technologies, Chantilly, VA) automated ELISA processor. We conducted a retrospective analysis of four years' worth of data, examining the percentage of indeterminate results and considering race, ethnicity, and reason for the outcome.
Results: Over 4 years, 17,743 individuals underwent testing for tuberculosis (TB). Out of all cases, 128 individuals had indeterminate results, which accounts for approximately 0.7% of the total cases. In the 128 cases examined, 53% of patients were female and 47% were male. The racial distribution was 41% African American and 59% non-African American. The indeterminate results were mainly due to various factors, such as 20% of the patients being immigrants, 59% being immunocompromised, 18% due to pre-analytical issues, and only 2% having TB-associated factors. 
Conclusion: Our data demonstrated that the contributing factors for indeterminates are majority of them are include a compromised immune system due to immunosuppressive therapy, the Bacille Calmette-Guérin vaccine in immigrants, and pre-analytical issues such as processing delays. 

Learning Objectives:

1.  Understand the Impact of Total Quality Initiatives in Clinical Laboratories 

2.  Identify Key Factors Leading to Indeterminate TB Test Results

3. Apply Best Practices to Reduce Indeterminate Outcomes in TB Testing