Combination of Blood Routine Examination and T-SPOT.TB Assay for Distinguishing Between Active Tuberculosis and Latent Tuberculosis Infection

Abstract

Background: Distinguishing between active tuberculosis (ATB) and latent tuberculosis infection (LTBI) remains challenging.

Methods: Between 2013 and 2019, 2,059 (1,097 ATB and 962 LTBI) and another 883 (372 ATB and 511 LTBI) participants were recruited based on positive T-SPOT.TB (T-SPOT) results from Qiaokou (training) and Caidian (validation) cohorts, respectively. Blood routine examination (BRE) was performed simultaneously. Diagnostic model was established according to multivariate logistic regression.

Results: Significant differences were observed in all indicators of BRE and T-SPOT assay between ATB and LTBI. Diagnostic model built on BRE showed area under the curve (AUC) of 0.846 and 0.850 for discriminating ATB from LTBI in the training and validation cohorts, respectively. Meanwhile, TB-specific antigens spot-forming cells (SFC) (the larger of early secreted antigenic target 6 and culture filtrate protein 10 SFC in T-SPOT assay) produced lower AUC of 0.775 and 0.800 in the training and validation cohorts, respectively. The diagnostic model based on combination of BRE and T-SPOT showed an AUC of 0.909 for differentiating ATB from LTBI, with 78.03% sensitivity and 90.23% specificity when a cutoff value of 0.587 was used in the training cohort. Application of the model to the validation cohort showed similar performance. The AUC, sensitivity, and specificity were 0.910, 78.23%, and 90.02%, respectively. Furthermore, we also assessed the performance of our model in differentiating ATB from LTBI with lung lesions. Receiver operating characteristic analysis showed that the AUC of established model was 0.885, while a threshold of 0.587 yield a sensitivity of 78.03% and a specificity of 85.69%, respectively.

Conclusions: The diagnostic model based on combination of BRE and T-SPOT could provide a reliable differentiation between ATB and LTBI.

Keywords: T-SPOT.TB; active tuberculosis; blood routine examination; diagnostic model; differential diagnosis; latent tuberculosis infection.

Figure 1

Establishment of diagnostic model based on combination of BRE and T-SPOT in Qiaokou cohort. (A) Scatter plots showing the score of diagnostic model based on BRE in ATB patients (n = 1,097) and LTBI individuals (n = 962) in Qiaokou cohort. Horizontal lines indicate the median. ***P < 0.001 (Mann-Whitney U test). Blue dotted lines indicate the cutoff value in distinguishing these two groups. (B) Scatter plots showing ESAT-6 SFC, CFP-10 SFC, and TBAg SFC in ATB patients (n = 1,097) and LTBI individuals (n = 962) in Qiaokou cohort. Horizontal lines indicate the median. ***P < 0.001 (Mann-Whitney U test). (C) ROC analysis showing the performance of ESAT-6 SFC, CFP-10 SFC, TBAg SFC, diagnostic model based on BRE, diagnostic based on combination of BRE and T-SPOT in distinguishing ATB from LTBI in Qiaokou cohort. (D) Venn diagrams showing the overlap of the diagnostic model based on BRE and TBAg SFC in ATB patients (n = 1,097) in Qiaokou cohort. (E) Scatter plots showing the score of diagnostic model based on combination of BRE and T-SPOT in ATB patients (n = 1,097) and LTBI individuals (n = 962) in Qiaokou cohort. Horizontal lines indicate the median. ***P < 0.001 (Mann-Whitney U test). Blue dotted lines indicate the cutoff values in distinguishing these two groups. ATB, active tuberculosis; LTBI, latent tuberculosis infection; ESAT-6, early secreted antigenic target 6; CFP-10, culture filtrate protein 10; TBAg, tuberculosis-specific antigens; SFC, spot-forming cells; AUC, area under the curve; BRE, blood routine examination.

Figure 2

Validation of diagnostic model based on combination of BRE and T-SPOT in Caidian cohort. (A) Scatter plots showing the score of diagnostic model based on BRE in ATB patients (n = 372) and LTBI individuals (n = 511) in Caidian cohort. Horizontal lines indicate the median. ***P < 0.001 (Mann-Whitney U test). Blue dotted lines indicate the cutoff value in distinguishing these two groups. (B) Scatter plots showing ESAT-6 SFC, CFP-10 SFC, and TBAg SFC in ATB patients (n = 372) and LTBI individuals (n = 511) in Caidian cohort. Horizontal lines indicate the median. ***P < 0.001 (Mann-Whitney U test). (C) ROC analysis showing the performance of ESAT-6 SFC, CFP-10 SFC, TBAg SFC, diagnostic model based on BRE, diagnostic based on combination of BRE and T-SPOT in distinguishing ATB from LTBI in Caidian cohort. (D) Venn diagrams showing the overlap of the diagnostic model based on BRE and TBAg SFC in ATB patients (n = 372) in Caidian cohort. (E) Scatter plots showing the score of diagnostic model based on combination of BRE and T-SPOT in ATB patients (n = 372) and LTBI individuals (n = 511) in Caidian cohort. Horizontal lines indicate the median. ***P < 0.001 (Mann-Whitney U test). Blue dotted lines indicate the cutoff values in distinguishing these two groups. ATB, active tuberculosis; LTBI, latent tuberculosis infection; ESAT-6, early secreted antigenic target 6; CFP-10, culture filtrate protein 10; TBAg, tuberculosis-specific antigens; SFC, spot-forming cells; AUC, area under the curve; BRE, blood routine examination.

Figure 3

The performance of established model for discriminating ATB from LTBI with pulmonary lesions. Scatter plots showing the score of the diagnostic model in ATB patients (n = 1,097) and LTBI individuals with pulmonary lesions (n = 671). Horizontal lines indicate the median. ***P < 0.001 (Mann-Whitney U test). Blue dotted lines indicate the cutoff value in distinguishing these two groups. ROC analysis showing the performance of the diagnostic model in distinguishing ATB from LTBI with pulmonary lesions. ATB, active tuberculosis; LTBI, latent tuberculosis infection; AUC, area under the curve.