Clinical application of T-spot test of Mycobacterium tuberculosis infection for diagnosis of suspected pulmonary tuberculosis patients / 解放军医学杂志

ABSTRACT

Objective To explore the application value of T-spot test of Mycobacterium tuberculosis infection (T-SPOT.TB) on diagnosis and differential diagnosis of pulmonary tuberculosis.Methods From Apr.2014 to Dec.2016,700 patients with suspected pulmonary tuberculosis were collected,venous blood (5ml) was drawn off and sputum was collected from each patient separately for T-SPOT.TB and pathogens identification (including TB).Chest CT,bronchoscopy brush or biopsy histopathological examination were followed up,cultivation of My.tuberculosis and of common bacteria with sputum or lavage fluid when needed.T-SPOT.TB test was performed according to the kit instruction operation.2.5 × 105 peripheral blood mononuclear cells (PBMCs) were added into the pre-coated anti-human γ-interferon antibody,and co-incubated separately with two specific My.tuberculosis antigens,namely early secretory targeting 6 (ESAT-6) and culture filtration protein 10 (CFP-10),and then the spot forming cells (SFCs) were counted.The gold standard for present study were set as follows1) My.tuberculosis smear positive or culture positive;2) Clinical diagnosis (meet any one is positive).The efficacy of T-SPOT.TB on diagnosing active TB was observed,and then the optimal critical value for diagnosing active TB was determined.Patients diagnosed as active TB were divided into 4 subgroupsinitial treatment group,retreatment group,smear or culture positive group,and smear or culture negative group.T-SPOT.TB was carried out to detect A and B antigen,and the difference of formed SFCs was then compared.The present study was approved by the Ethics Committee of Xinjiang Uygur Autonomous Region Chest Hospital.Results Of 700 cases suspected of pulmonary tuberculosis enrolled in present study,528 out of 624 definite cases (84.6％) were finally diagnosed as active tuberculosis (active TB group) and 96 cases (15.4％) were as without TB infection (non-TB group).Positive results of T-SPOT.TB test were found in 414 cases in active TB group,and 47 cases in non-TB group were reported with T-SPOT.TB negative.The sensitivity and specificity of T-SPOT.TB test for diagnosing active TB were 78.4％ and 49％,respectively.The positive predictive value,negative predictive value,positive likelihood ratio and negative likelihood ratio were 89.4％,29.2％,1.537 and 0.441,respectively.ROC curve showed that the specificity increased significantly (from 49％ to 62.5％) while the sensitivity decreased (from 78.4％ to 72.7％) when antigen A (cut-off16.0 SFCs/2.5 × 105 PBMC) was combined with antigen B (cut-off7.0 SFCs/2.5 × 105 PBMC) for analysis.In addition,the number of A and B antigen spots in active TB group was significantly higher than that in non-TB group (P＜0.01).The number of B antigen spots in positive TB group was significantly higher than that in negative TB group (P＜0.05).There was no significant difference among the other groups.Conclusions Since the high sensitivity and low specificity of T-SPOT.TB in the diagnosis of active TB,the final diagnosis should be combined with clinical manifestations.When the A antigen is 16.0 SFCs/2.5 × 105 PBMC and the B antigen is 7.0 SFCs/2.5 × 105 PBMC,the specificity of T-SPOT.TB will be improved.Higher number of spots has a certain reference diagnostic value for active TB.