Challenges in the development of an immunochromatographic interferon-gamma test for diagnosis of pleural tuberculosis.

Existing diagnostic tests for pleural tuberculosis (TB) have inadequate accuracy and/or turnaround time. Interferon-gamma (IFNg) has been identified in many studies as a biomarker for pleural TB. Our objective was to develop a lateral flow, immunochromatographic test (ICT) based on this biomarker and to evaluate the test in a clinical cohort. Because IFNg is commonly present in non-TB pleural effusions in low amounts, a diagnostic IFNg-threshold was first defined with an enzyme-linked immunosorbent assay (ELISA) for IFNg in samples from 38 patients with a confirmed clinical diagnosis (cut-off of 300 pg/ml; 94% sensitivity and 93% specificity). The ICT was then designed; however, its achievable limit of detection (5000 pg/ml) was over 10-fold higher than that of the ELISA. After several iterations in development, the prototype ICT assay for IFNg had a sensitivity of 69% (95% confidence interval (CI): 50-83) and a specificity of 94% (95% CI: 81-99%) compared to ELISA on frozen samples. Evaluation of the prototype in a prospective clinical cohort (72 patients) on fresh pleural fluid samples, in comparison to a composite reference standard (including histopathological and microbiologic test results), showed that the prototype had 65% sensitivity (95% CI: 44-83) and 89% specificity (95% CI: 74-97). Discordant results were observed in 15% of samples if testing was repeated after one freezing and thawing step. Inter-rater variability was limited (3%; 1 out of 32). In conclusion, despite an iterative development and optimization process, the performance of the IFNg ICT remained lower than what could be expected from the published literature on IFNg as a biomarker in pleural fluid. Further improvements in the limit of detection of an ICT for IFNg, and possibly combination of IFNg with other biomarkers such as adenosine deaminase, are necessary for such a test to be of value in the evaluation of pleural tuberculosis.

Evaluation of real-time polymerase chain reaction, interferon-gamma, adenosine deaminase, and immunoglobulin A for the efficient diagnosis of pleural tuberculosis.

OBJECTIVE: Pleural tuberculosis (TB) is a diagnostic challenge because of its non-specific clinical presentation and paucibacillary nature. Conventional diagnosis methods have limitations. We evaluated the real-time polymerase chain reaction (PCR), interferon-gamma (IFN-γ), adenosine deaminase (ADA), and immunoglobulin A (IgA). METHODS: We assessed 204 cases: 50 were confirmed pleural TB, 104 were probable pleural TB, and 50 formed the non-TB group. IFN-γ and IgA were measured by enzyme-linked immunosorbent assay and ADA was measured by colorimetric assay. Real-time PCR was carried out using the 16S rRNA sequence, pleural biopsy specimens were submitted to histopathologic examination, pleural fluid culture was undertaken using Lowenstein-Jensen and MGIT-BACTEC, and pleural fluid smears were stained with auramine O. RESULTS: For confirmed and probable pleural TB cases, the area under the curve (AUC) of the receiver operating characteristic (ROC) curve was highest for IFN-γ (0.994 and 0.963, respectively), followed by ADA (0.989 and 0.945, respectively), real-time PCR (0.898 and 0.784, respectively), and IgA (0.817 and 0.784, respectively). For confirmed and probable pleural TB cases, IFN-γ showed the highest sensitivity (98% and 76.9%, respectively), followed by ADA (92% and 73%, respectively), real-time PCR (80% and 57.7%, respectively), and IgA (70% and 57.7%, respectively). With regard to combined positivity, the combination of 'either real-time PCR or IFN-γ' showed the highest sensitivity: 100% in confirmed pleural TB and 96.2% in probable pleural TB. CONCLUSIONS: IFN-γ showed the highest sensitivity as an individual diagnostic test. When a combination of tests was used, positivity of 'either IFN-γ or real-time PCR' appeared valuable for the diagnosis of pleural TB.

Evaluation of whole blood IFNgamma test using PPD and recombinant antigen challenge for diagnosis of pulmonary and extra-pulmonary tuberculosis.

Quantiferon TB gold (QFT-G) with recombinant antigen cocktail is well evaluated for diagnosis of pulmonary tuberculosis (PTB). However, diagnosis of extra-pulmonary tuberculosis (EPTB) is more difficult due to limitations of conventional techniques. This study compares recombinant antigens based QFT-G and low cost PPD based interferon test for the diagnosis of PTB and EPTB. IFNgamma release, with recombinant antigens and PPD, was assayed by ELISA from 140 cases of EPTB, 100 cases of PTB along with acid fast bacillus (AFB) detection, AFB culture on LJ and MGIT BACTEC. Sensitivity and specificity for QFT-G recombinant antigens was 84.29% and 96%, while for PPD based interferon was 70% and 84% for EPTB group. The sensitivity was far superior to AFB smear and culture for both the antigens. Nine samples were identified as non-tubercular mycobacteria (NTM) in the EPTB group and all were negative for QFT-G, but six of them were positive for PPD based test. Results of the study show that QFT-G using recombinant antigen is sensitive and specific for both PTB and EPTB diagnosis. The PPD based test is economic and offers comparable performance for PTB and EPTB diagnosis and also useful for diagnosis of NTM.

Role of cancer antigen-125 from pleural & ascitic fluid samples in non malignant conditions.

BACKGROUND & OBJECTIVE: CA-125, an ovarian tumor marker is known to increase in non malignant conditions such as tubercular and non tubercular pleuritis and ascites. We undertook this study to evaluate non-specific rise in CA-125 levels in conditions associated with pleural effusion and ascites and also to understand the mechanism of its secretion. METHODS: CA-125 levels in 38 pleural and 46 ascitic fluid samples from non malignant cases and 10 blood samples from pulmonary tuberculosis cases were estimated by ELISA. The ascitic fluid samples were collected from cases of bacterial peritonitis, tuberculosis, hepatitis, cirrhosis of other aetiology and pleural fluid samples were from cases of tubercular, pyogenic, cardiomegaly and other conditions. RESULTS: Both ascitic and pleural fluid samples (transudative and exudative) showed elevated CA- 125 levels. The CA-125 levels were significantly higher in ascitic fluid samples than in pleural fluid samples. INTERPRETATION & CONCLUSION: Our findings showed that elevated levels of CA-125 in pleural and ascitic fluid could be because of varied aetiologies which need to be ruled out before considering malignancy. Peritoneum has a greater capacity to secrete CA-125 than the pleural epithelium and the secretion occurs following inflammation or mechanical distress. Pulmonary tuberculosis as a closed lesion without involvement of pleural epithelium does not evoke high CA-125 release.

Chronic knee monoarthritis caused by Mycobacterium chelonae.

Extrapulmonary tuberculosis occurs in 20% of all patients with tuberculosis and tubercular arthritis occurs in 10% of those with extrapulmonary tuberculosis. Arthritis caused by Mycobacterium tuberculosis is not uncommon in India. However, arthritis caused by Mycobacterium chelonae has not been reported to the best of our knowledge. We report a patient with arthritis caused by Mycobacterium chelonae in whom the diagnosis was confirmed by smear and culture of acid-fast bacilli. Polymerase chain reaction of the synovial fluid using IS6110 was negative.