Background/Purpose: The Quantiferon test (QFT) is used to for screen for tuberculosis in patients with autoinflammatory conditions (IC) prior to the use of  immunosuppressant medications.  Indeterminate results limit the utility of QFT and strategies are need to reduce their impact on the diagnostic progress.  The aim of this study was 1) To analyze the rate of indeterminate QFT in patients with IC as compared to both the general hospital population and a healthy reference (HR) group, and 2) To analyze factors contributing to an indeterminate test result.

Methods: Adults (≥18 years) with a QFT result within the Cleveland Clinic Health System electronic medical record between 2007–2012 were included.  Patients were categorized as having IC if any of the following conditions were present in the year preceding their first QFT: rheumatoid arthritis, psoriatic arthritis, systemic vasculitis, inflammatory bowel disease, inflammatory spondylarthropathy, or systemic lupus erythematous. Subjects who did not have an IC receiving their QFT at a corporate health screening center were considered the HR group of hospital employees, with all others receiving the QFT considered the general hospital population. Prevalent use of glucocorticoids (GC), biologics, or disease modifying anti-rheumatic drugs (DMARDs) or cessation within 5 days of QFT was used to evaluate the effect of these drug classes on indeterminate tests in the IC group. Binomial regression was used to estimate the risk of having an indeterminate test result, adjusting for age, gender, co-morbidities (Human immunodeficiency virus, chronic kidney disease, diabetes mellitus, chronic obstructive pulmonary disease, and asthma), and health services use in the prior year.

Results: Of the 55,132 included patients, 5.2% had inflammatory conditions and 46.6 % were employees. The mean age of patients in our sample was 40.2 years and 68.5% were female.  Indeterminate tests were present in 5.3% of the IC group, 1.9% of the general hospital population, and 1.5% of the HR group. Patients with IC were 3.6 times as likely as the HR group to have indeterminate test results (adjusted risk ratio (aRR): 3.60, 95%CI: 3.00, 4.30). There was no significant difference between the general  hospital population and the HR group.  In adjusted models restricted to patients with IC, GC use significantly increased the likelihood of an indeterminate test (aRR:1.43, 95%CI: 1.02, 1.99) while DMARD use decreased this likelihood (aRR: 0.67, 95%CI: 0.46, 0.97) when compared to patients without medication use.

Conclusion: Patients with autoinflammatory conditions were more likely to have indeterminate QFT results as compared with a reference group of hospital employees. Among patients with IC, only prior use of GC was associated with an increase in the likelihood of having an indeterminate test result.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/evaluating-indeterminate-quantiferon-tb-gold-in-tube-results-in-patients-with-chronic-inflammatory-diseases-on-immunosuppressive-therapy/