Health Technology Assessment 2007; Vol 11: number 3
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J Dinnes,1* J Deeks,2 H Kunst,3 A Gibson,4 E Cummins,5 N Waugh,6 F Drobniewski4 and A Lalvani7
1 Wessex Institute for Health Research and Development, University of Southampton, UK
2 Centre for Statistics in Medicine, University of Oxford, UK
3 Department of Respiratory Medicine, Royal Brompton Hospital, London, UK
4 HPA National Mycobacterium Reference Unit, London, UK
5 McMaster Development Consultants, Glasgow, UK
6 Department of Public Health, University of Aberdeen, UK
7 Nuffield Department of Clinical Medicine, University of Oxford, UK
* Corresponding author
Globally, there are 8 million new tuberculosis (TB) cases and 2 million deaths per year. Once infected, active disease develops in about 10% of cases, usually within 12 years after exposure. Remaining individuals enter into a state of latentcy [latent tuberculosis infection (LTBI)], which can reactivate at a later stage, particularly if the individual becomes immunocompromised.
Active TB is predominantly pulmonary in nature. Extra-pulmonary TB occurs in approximately 41% of TB cases in England and Wales and includes lymphatic, pleural, meningeal, pericardial, skeletal, gastrointestinal, genitourinary and miliary TB. LTBI has no clinical manifestations and is not contagious.
Given the infectious nature of pulmonary TB, fast and accurate diagnosis is an important element of TB treatment and control.
Literature was identified from electronic databases and other sources. All databases were searched from 1975 to August 2003 for tests for active TB and to March 2004 for tests for LTBI. Reference lists of included studies and relevant review articles were scanned for additional studies.
Any study comparing a rapid test for detection of active tuberculosis with any reference standard was included. ‘Rapid’ tests were those for which a result could be obtained in less than the time taken for standard culture. Only case series studies were included. Accuracy studies had to report sufficient information to allow the construction of a 2 × 2 contingency table.
The study selection criteria were (1) testing for LTBI, (2) comparison between tuberculin skin test (TST) and interferon-γ assays based on ESAT-6 and CFP-10 antigens and (3) information on TB exposure or bacille CalmetteGuérin (BCG) vaccination or HIV status.
Data extraction and study quality assessment were undertaken independently by two reviewers.
For each test comparison, the sensitivity, specificity and 95% confidence intervals (CIs) were calculated. The method proposed by Moses and colleagues to fit both symmetric and asymmetric summary receiver operating characteristic (SROC) curves was used. Sources of heterogeneity were investigated by adding covariates to the standard regression model.
Interferon-γ assays were examined to establish whether they were more strongly associated with high versus low TB exposure than TST. Odds ratios (ORs) were calculated for the association between test results and exposures from each study along with their 95% CIs. Within each study, the OR value for one test was divided by that for another to produce a ratio of OR (ROR).
A total of 212 studies were included, providing 368 data sets. A further 19 studies assessing fully automated liquid culture were included.
Overall, nucleic acid amplification test (NAAT) accuracy was far superior when applied to respiratory samples as opposed to other body fluids. The better quality in-house studies were, for pulmonary TB, much better at ruling out TB than the commercial tests (higher sensitivity), but were less good at ruling it in (lower specificity), but it is not possible to recommend any one over another owing to a lack of direct test comparisons.
The specificity of NAAT tests was high when applied to body fluids, for example for TB meningitis and pleural TB, but sensitivity was poor, indicating that these tests cannot be used reliably to rule out TB. High specificity estimates suggest that NAAT tests should be the first-line test for ruling in TB meningitis, but that they need to be combined with the result of other tests in order to rule out disease. Evidence for NAAT tests in other forms of TB and for phage-based tests is significantly less prolific than for those above and further research is needed to establish accuracy.
There is no evidence to support the use of adenosine deaminase (ADA) tests for diagnosis of pulmonary TB; however, there is considerable evidence to support their use for diagnosis of pleural TB and to a slightly lesser extent for TB meningitis.
Anti-TB antibody test performance was universally poor, regardless of type of TB. Fully automated liquid culture methods were superior to culture on solid media, in terms of their speed and their precision.
In total, 13 studies were included. Assays based on RD1-specific antigens, ESAT-6 or CFP-10, correlate better with intensity of exposure, and therefore are more likely than TST/purified protein derivative (PPD)-based assays to detect LTBI accurately. An additional advantage is that they are more likely to be independent of BCG vaccination status and HIV status.
The NAAT tests provide a reliable way of increasing the specificity of diagnosis (ruling in disease) but sensitivity is too poor to rule out disease, especially in smear-negative (paucibacillary) disease where clinical diagnosis is equivocal and where the clinical need is greatest.
For extra-pulmonary TB, clinical judgement has both poor sensitivity and specificity. For pleural TB and TB meningitis, adenosine deaminase tests have high sensitivity but limited specificity. NAATs have high specificity and could be used alongside ADA (or interferon-γ) to increase sensitivity for ruling out disease and NAAT for high specificity to rule it in.
All studies from low-prevalence countries strongly suggest that the RD1 antigen-based assays are more accurate than TST- and PPD-based assays for diagnosis of LTBI. If their superior diagnostic capability is found to hold up in routine clinical practice, they could confer several advantages on TB control programmes.
Diagnostic accuracy must be established, preferably prospectively, in a wide spectrum of patients, against an appropriate reference test, and avoiding the major sources of bias such as verification bias, lack of blinding, and inclusion of all indeterminate results.
Dinnes J, Deeks J, Kunst H, Gibson A, Cummins E, Waugh N, et al. A systematic review of rapid diagnostic tests for the detection of tuberculosis infection. Health Technol Assess 2007;11(3).
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