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PROSPECTIVE EVALUATION OF A NEW SEROLOGIC TEST (ASSURE TB RAPID TEST) FOR DIAGNOSIS OF PULMONARY TUBERCULOSIS

National University Hospital, Singapore, Singapore

PURPOSE: Case detection and early treatment of positive patients are critical to the control of pulmonary tuberculosis (PTB). Traditionally, diagnosis of tuberculosis depends on smear-culture method which although considered "gold standard" leaves a lot to be desired. We prospectively compared ASSURE^TM TB Rapid Test (Genelabs Diagnostics), which is a rapid tuberculosis serologic test, with traditional approaches for diagnosis of pulmonary tuberculosis.

METHODS: We enrolled all consecutive adult patients (18 years of age) suspected of having active PTB between June 2001 and March 2003.All patients were tested for 3 sputum samples (or tracheal aspirate in intubated patients) for smear and culture of Mycobacterium tuberculosis (MTB). ASSURE^TM TB Rapid Test was done within 3 days of the sputum sampling.

RESULTS: A total number of 238 patients were included. Of these 171 patients were male and 67 female (2.5:1) with a mean age of 56.6 (18-96, ±18.4) years. Twenty-two patients were excluded because culture either showed Mycobacteria Other Than Tuberculosis (MOTT, 9), or were contaminated (7) or were not done (6). Final analysis therefore included 216 patients. The sensitivity and specificity of the new serological test were 60.2% (95% CI, 50.5 - 69.1%) and 82.3% (95% CI, 74.2-88.2%) respectively in relation to the final diagnosis in contrast to those of the smear test, which were 53.4%(95% CI, 43.8-62.7%) and 98.2% (95% CI, 93.8-99.5%). Combination of the sputum smear and serology provides an increased sensitivity of 74.8% (95% CI, 65.6-82.2%) but a relatively lower specificity of 80.5%(95% CI, 72.3-86.8%) with the tested cohort of high TB prevalence.

CONCLUSION: 1)A moderate increase in sensitivity but a decrease in specificity were observed with the new test in comparison with the direct smear examination, 2) Combination of the sputum smear and the new serology increased further the sensitivity while maintain a moderate specificity with the tested cohort.

CLINICAL IMPLICATIONS: ASSURE^TMTB Rapid Test is not beneficial if used alone as a tool for rapid diagnosis of PTB but can improve case-detection when combined with smear test.

Final Diagnosis PTB Non-TB Sensitivity Specificity Smear     Positive (%) 57 (26.4) 55 2 53.4 98.2     Negative (%) 159 (73.6) 48 111 Serology     Positive (%) 82 (38) 62 20 60.2 82.3     Negative (%) 134 (62) 41 93 Smear & Serology     Positive (%) 99 (45.8) 77 22 74.8 80.5     Negative (%) 117 (54.2) 26 91

DISCLOSURE: Amartya Mukhopadhyay, None.