Per consensus guidelines from the Centers for Disease Control and Prevention (CDC) and Infectious Diseases Society of America (IDSA), the sensitivity of interferon-gamma release assays (IGRAs) are consistently found to be equal (Quantiferon, 81-86%) or superior (T-spot, 90-95%) to the sensitivity of tuberculosis skin testing (71-82%). In patients who were vaccinated with BCG, IGRAs and tuberculosis skin tests appear to be similar. A meta-analysis found the specificity of Quantiferon to be >95% in patients vaccinated with BCG; however, data is more limited for the T-spot test in these patients. The sensitivity of IGRAs, both Quantiferon and T-spot, in persons with HIV is estimated to range from 65% to 100%. The guidelines do not recommend one test over another; instead, they discuss IGRA tests as a whole versus skin testing. 
A 2018 prospective comparative study (Table 1) assessed the diagnostic performance of the QuantiFERON-TB Gold In-Tube test and T-SPOT.TB assays in 746 patients with active tuberculosis (TB) and compared the concordance in routine clinical practice in a setting with high tuberculosis rates. Sensitivities for the T-spot assay were 88.6% (95% confidence interval [CI] 83.3 to 92.5) in the confirmed TB group and 83.1% (95% CI 78.4 to 87) in the group with probable TB. Sensitivities for the Quantiferon test were 88.4% (95% CI 82.9 to 92.3) in the confirmed TB group and 82.5% (95% CI 77.6 to 86.5%) in the group of patients with probable TB. T-spot had a specificity of 63.4% (95% CI 57.4 to 69) compared to 60.5% (95% CI 82.9 to 92.3) with Quantiferon in patients with no TB. Sensitivity and specificity values were higher for the T-spot, but none of these values were significantly different. The T-spot assay resulted in significantly fewer indeterminate test results (0.4%) compared to the Quantiferon (4.3%; p<0.001). There was a 92.3% agreement between the tests. The results show there may be small differences in the accurate diagnosis of tuberculosis with T-spot and Quantiferon, but the differences are unlikely to be significant. 
A retrospective analysis assessed the relevance of age on the sensitivity of interferon-gamma release assays (Quantiferon [N=192] or T-spot test [N=212]). The positivity of the test was compared to a true infection as defined by a positive culture or PCR. The overall sensitivity of the Quantiferon test was 80.2%, while the overall sensitivity of the T-spot test was 91.0%. The sensitivities of Quantiferon and T-spot, respectively, according to age group were as follows: <29 years, 93.3% and 96.7%; 30–49 years, 86.5% and 94.7%; 50–69 years, 76.8% and 87.5%; and >70 years, 68.3% and 85.7%, respectively. The trend of age-related changes in sensitivity was significant for both tests (p = 0.039). However, only Quantiferon was significantly related to age in the multivariate analysis. The authors conclude Quantiferon, but not T-spot, was significantly affected by patient age. 
A 2006 prospective study enrolled 393 patients to compare the efficacy of two commercial blood assays, T-SPOT.TB and QuantiFERON-TB Gold, with the tuberculin skin test in patients with suspected latent or active tuberculosis. Overall, both tests had a similar agreement with the skin test; however, Quantiferon was associated with more indeterminate results than with T-spot (11% vs 3%; p <0.0001). Age ≤ 5 years was one of the identified factors related to indeterminate results with Quantiferon (p=0.003), but not with T-spot. Immunosuppressive treatments were also contributory to indeterminate results for both tests. Significantly higher rates of positive results were seen in T-spot than in Quantiferon (38% vs 26%; p <0.0001). Notably, individuals who had close contact with active tuberculosis were less likely to test positive with Quantiferon than with T-spot (p = 0.001). In conclusion, the authors emphasized that in routine clinical practice T-spot and Quantiferon might provide different results.