Background: An antibody detection-based diagnostic test in a user-friendly format could potentially replace microscopy and extend tuberculosis diagnosis to lower levels of health services. Dozens of commercial serological tests for tuberculosis are being marketed in many parts of the world, despite previous systematic reviews having reported variable sensitivity and specificity of these tests. Since the publication of these reviews, the evidence base has grown, methods for meta-analyses of diagnostic tests have evolved, and the WHO Stop TB Department (STB) has implemented a systematic approach to evidence synthesis for TB diagnostic policy development involving systematic reviews and meta-analyses, assessment of the evidence base by Expert Group review, and implementation of the GRADE process for evidence synthesis.
Methods: An updated systematic review was commissioned to synthesize the evidence on the diagnostic accuracy of commercial serological tests for pulmonary and extrapulmonary tuberculosis. Database searches for relevant studies in all languages were updated through May 2010 and a bivariate meta-analysis was performed that jointly models both test sensitivity and specificity. The findings were presented to an independent WHO Expert Group and the evidence assessed using the GRADE approach. As conflict of interest in diagnostic studies is a known concern the systematic review also evaluated the involvement of commercial test manufacturers in published studies.
Results: For pulmonary tuberculosis, 67 unique studies were identified, including 32 studies from low- and middle-income countries. None of these studies evaluated the tests in children. The results demonstrated that (1) for all commercial tests, sensitivity (0% to 100%) and specificity (31% to 100%) from individual studies were highly variable; (2) using bivariate meta-analysis for Anda-TB IgG (the most commonly evaluated test), the pooled sensitivity was 76% (95% CI 63% to 87%) in studies of smear-positive and 59% (95% CI 10% to 96%) in studies of smear-negative patients, respectively; the pooled specificity in these studies was similar: 92% (95% CI 74% to 98%) and 91% (95% CI 79% to 96%), respectively; (3) for Anda-TB IgG, sensitivity values in smear-positive (54% to 85%) and smear-negative (35% to 73% ) patients from individual studies were highly variable; (4) for Anda-TB IgG, specificity values from individual studies were variable (68% to 100%); (5) a TDR evaluation of 19 rapid commercial tests, in comparison with culture plus clinical follow-up, showed similar variability with sensitivity values of 1% to 60% and specificity of 53% to 99%; (6) compared with ELISAs [60% (95% CI 6% to 65%], immuno-chromatographic assays had lower sensitivity [53%, 95% CI 42% to 64%]; and (7) in a single study involving HIV-infected TB patients, the sensitivity of the SDHO test was 16% (95% CI 5% to 34%).
For extrapulmonary tuberculosis, 25 unique studies were identified, including 10 studies from low- and middle-income countries. None of these studies evaluated the tests in children. The results demonstrated that (1) for all commercial tests, sensitivity (0% to 100%) and specificity (59% to 100%) values from individual studies were highly variable; (2) pooled sensitivity was 64% (95% CI 28% to 92%) for lymph node tuberculosis and 46% (95% CI 29% to 63%) for pleural tuberculosis; (3) for Anda-TB IgG, the pooled sensitivity and specificity were 81% (95% CI 49% to 97%) and 85% (95% CI 77% to 92%) respectively while sensitivity (26% to 100%) and specificity (59% to 100%) values from individual studies were highly variable; and (5) in one study involving HIV-infected TB patients, the sensitivity of the MycoDot test was 33% (95% CI 19% to 39%).
The vast majority of studies were either sponsored by industry, involved commercial test manufacturers, or failed to provide information on industry sponsorship.
Conclusions: Commercial serological tests provide inconsistent and imprecise findings resulting in highly variable values for sensitivity and specificity. There is no evidence that existing commercial serological assays improve patient-important outcomes, and high proportions of false-positive and false-negative results adversely impact patient safety. Overall data quality was graded as very low and it is strongly recommended that these tests not be used for the diagnosis of pulmonary and extra-pulmonary TB.
