Methods: We prospectively recruited HIV-positive adult patients with CD4 count less than or equal to 200/mm3 and symptoms suspected of active TB from two tertiary hospitals between December 2015 and March 2017. Freshly collected urine was applied to the Determine®-TB LAM Ag test strip (4 bands of graded intensity), using grade 1 cut-off. Diagnostic accuracy of urine LAM strip test were assessed against microbiological reference standard, defined as positive Mycobacterium tuberculosis cultured from one or more clinical specimens (definite TB) or composite reference standard including definite TB and probable TB, defined as those have symptoms consistent with TB and response to anti-TB treatment.
Results: A total of 280 patients were enrolled. Of whom, 72 (25.7%) and 65 (23.2%) had definite and probable TB. Amongst those with definite TB, LF-LAM test gave a sensitivity of 75.0% (95% CI 63.9-83.6), specificity of 86.0% (95% CI 79.4-90.8) and accuracy of 82.3% (95% CI 76.7-86.8). When compared with the composite reference standard, the test yielded a lower sensitivity (61.3%, 95% CI 53.0-69.1) and accuracy (73.9%, 95% CI 68.5-78.7), with equal specificity. The test showed the highest sensitivity (90.5%, 95% CI 77.9-96.2) and accuracy (85.9%, 95% CI 79.2-90.7) but lower specificity (84.0%, 95% CI 75.6-89.9) in HIV-infected patients with CD4 count less than 50/mm3. The sensitivity of the combined LF-LAM or sputum microscopy was higher than that of either test alone (86.1% vs. 75.0%, 61.1%, respectively). Mycobacterium avium complex (MAC) was cultured in 7 out of 20 with false positive result. Urine LAM strip test can remain positive for up to 4 weeks even after anti-TB treatment.
Conclusion: Urine LAM assay gave the best performance for diagnosis of active TB in advanced HIV-infected patients and provide an additional benefit of a greater simplicity, speed, with a more easily obtainable sample.
M. Na Songkhla,
S. Tongsai, None
N. Angkasekwinai, None