Factors Influencing the Indeterminate Results in a T-SPOT.TB test: A Matched Case-control Study

• Published in: Internal Medicine Vol. 62; no. 22; pp. 3321 - 3326
• Main Authors: Herai, Yoriko, Yahaba, Misuzu, Taniguchi, Toshibumi, Murata, Shota, Chiba, Hitoshi, Igari, Hidetoshi
• Format: Journal Article
• Language: English
• Published: Japan The Japanese Society of Internal Medicine 15.11.2023; Japan Science and Technology Agency
• Subjects: Case-Control Studies; high nil-control; HTLV-1; Human T-lymphotropic virus 1; Humans; indeterminate; Interferon-gamma; Interferon-gamma Release Tests; Internal medicine; low mitogen-control; Lymphocytes T; Mitogens; Original; Retrospective Studies; Statistical analysis; Tuberculin Test; γ-Interferon; high nil-control; low mitogen-control; HTLV-1; indeterminate
• ISSN: 0918-2918; 1349-7235
• DOI: 10.2169/internalmedicine.1006-22

Objective A T-SPOT.TB can yield indeterminate results under two test observation conditions: a high response to the nil in negative control wells (high nil-control) or a low response to the mitogen in positive control wells (low mitogen-control). The most strongly influential factors for these indeterminate results, however, have yet to be identified. Methods From June 1, 2015, to June 30, 2021, we conducted a 1:1 matched case-control, retrospective study. Patients Patients who underwent a T-SPOT.TB test at Chiba University Hospital. Results The study included 5,956 participants. Indeterminate results were found in 63 participants (1.1%), including high nil-control in 37 and low mitogen-control in 26. Human T-cell leukemia virus type 1 (HTLV-1) positivity was the only influencing factor associated with high nil-control (adjusted odds ratio=98.5, 95% confidence interval: 6.59-1,480). Conclusion Regarding the indeterminate results, all HTLV-1 positive participants had a high nil response and no low mitogen response. It was suspected that abnormally produced interferon γ caused a nonspecific reaction to the negative control well, resulting in a high nil response. Low mitogen-control, conversely, did not appear to have any statistically significant influential factors.