Introduction: While QuantiFERON-TB gold (QFT) is frequently used, little attention is paid to the mitogen response. How it could be impacted and associated with outcomes is poorly known.
Methods: Retrospective, case-control study in hospitalized patients who underwent QFT testing in two hospitals between 2016 and 2019. We defined two groups of cases with either negative [interferon (IFN)-γ ≤ 0.5 IU/ml, official threshold] or weak (0.5-2 IU/ml) mitogen response, and one group of controls with normal (>2 IU/ml) mitogen response.
Results: A total of 872 patients were included. An ongoing infection was independently associated with both a negative (RR = 4.34; 95% CI = 2.94-6.41) and a weak mitogen response (RR = 2.44; 95% CI = 1.66-3.58). Among tuberculosis patients, a weak mitogen response was associated with a false-negative QFT result (75%) compared to a normal response (20%). Decreasing mitogen response (normal, weak and negative, respectively) was associated with increasing length of hospital stay [median (interquartile range) 5 (3-13), 11 (5-21) and 15 (10-30) days; p < 0.001] and increasing hospital mortality (3, 7, and 15%; p < 0.001).
Conclusion: Clinicians should take notice of the mitogen response since IFN-γ concentrations lower than <2 IU/ml were associated with false-negative QFT results in tuberculosis patients, independently associated with ongoing infections, and could be associated with worse prognosis.
Keywords: QuantiFERON; infection; mitogen; mortality; outcomes.
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