Background: Xpert MTB/RIF (‘Xpert’) and urinary lipoarabinomannan (LAM) assays offer rapid tuberculosis (TB) diagnosis, but have suboptimal sensitivity when used individually in HIV-positive patients. The yield of these tests used in combination for the diagnosis of active TB among HIV-infected TB suspects is unknown.
Design: Study of comparative diagnostic accuracy nested into a prospective study of HIV-infected individuals with signs and/or symptoms of TB in Uganda.
Methods: Xpert testing of archived sputum was conducted for culture-confirmed TB cases and TB suspects in whom a diagnosis of TB was excluded. Additional testing included sputum smear microscopy, sputum culture (solid and liquid media), mycobacterial blood culture, and urinary testing for LAM using a lateral flow test (‘LF-LAM’) and an enzyme-linked immunosorbance assay (‘ELISA-LAM’).
Results: Among 103 participants with culture-confirmed TB, sensitivity of Xpert was 76% (95% confidence interval, CI 0.66–0.84), and was superior to that of LF-LAM (49%, 95% CI 0.39–0.59, P < 0.001). Specificity was greater than 97% for both tests among 105 individuals without TB. The combination of smear microscopy and LF-LAM identified 67% (95% CI 0.57–0.76) of culture-confirmed TB cases and approached sensitivity of Xpert testing alone (P = 0.15). The sensitivity of the combination of Xpert and LF-LAM was 85% (88/103 95% CI 0.77–0.92), which was superior to either test alone (P < 0.05) and approached sensitivity of sputum liquid culture testing (94%, 95% CI 0.88–0.98, P = 0.17).
Conclusion: Sputum Xpert and urinary LAM assays were complementary for the diagnosis of active TB in HIV-infected patients, and sensitivity of the combination of these tests was superior to that of either test alone.
aJohns Hopkins University School of Medicine, Baltimore, Maryland, USA
bDepartment of Microbiology
cInfectious Diseases Institute, Makerere University College of Health Sciences, Kampala, Uganda
dBoston Medical Center, Boston University School of Medicine, Boston, Massachusetts, USA.
Correspondence to Maunank Shah, MD, Johns Hopkins University School of Medicine, 1503 East Jefferson St, Room 118, Baltimore, MD 21231, USA. Tel: +1 443 287 0401; fax: +1 410 955 0740; e-mail: firstname.lastname@example.org
Received 11 February, 2014
Revised 24 February, 2014
Accepted 24 February, 2014