Predictive factors for indeterminate result on the QuantiFERON test in an intermediate tuberculosis-burden country

Objectives: The QuantiFERON-TB Gold In-Tube (QFT-G IT) test is based on the cellular immune response, and this assay can result in indeterminate results for the diagnosis of tuberculosis. The occurrence of indeterminate results may decrease the clinical usefulness of this test. Therefore, we investigated possible predictive factors that can influence the occurrence of indeterminate results from the QFT-G IT test. Methods: We conducted a case-control study with 162 case patients who had indeterminate results from a QFT-G IT test at a tertiary hospital in South Korea, from September 2006 to September 2009. Results: Of the 1276 patients, 162 (12.7%) cases that underwent QFT-G IT testing were reported as indeterminate results. Severe lymphopenia (odds ratio [OR] = 8.839; p < 0.001), chronic renal disease (OR = 2.838; p = 0.007), autoimmune disease (OR = 2.527; p = 0.017) and chronic lung disease (OR = 3.169; p = 0.007) were independent predictive factors for indeterminate results from a QFT-G IT test. Conclusion: The patients with lower lymphocyte counts or immunosuppressive conditions showed a higher probability of indeterminate results from the QFT-G IT test. Careful attention to the pre-analytical conditions may be able to minimize this proportion.