Two rapid TB diagnostic tests had greater sensitivity in diagnosing tuberculosis in HIV-positive Ugandan, according to results of a 103-patient study. Sensitivity of the combined tests approached that of sputum liquid culture testing.
Xpert MTB/RIF and urinary lipoarabinomannan (LAM) assays offer rapid diagnosis of TB. But their sensitivity—the ability to confirm positive cases as positive—is low compared with sputum liquid culture testing. Because the combined sensitivity of Xpert and LAM were unknown, researchers conducted this comparative analysis in HIV-positive Ugandans with signs or symptoms of TB.
The analysis involved archived sputum of HIV-positive patients tested with Xpert, lateral-flow (LF)-LAM, enzyme-linked immunosorbance LAM, sputum smear microscopy, sputum culture (solid and liquid media), and mycobacterial blood culture.
In 103 HIV patients with culture-confirmed TB, Xpert TB sensitivity was 76% (95% confidence interval [CI] 0.66 to 0.84), significantly exceeding the sensitivity of LF-LAM (49%, 95% CI 0.39 to 0.59, P < 0.001). Specificity—the ability of a test to identify negative patients as negative—exceeded 97% for Xpert and LF-LAM in 105 people without TB.
Smear microscopy plus LF-LAM had a sensitivity of 67% (95% CI 0.57 to 0.76) for culture-confirmed TB, approaching the 76% sensitivity of Xpert alone (P = 0.15). Xpert plus LF-LAM had a sensitivity of 85% (95% CI 0.77 to 0.92), significantly greater than the sensitivity of either test alone (P < 0.05) and approaching the sensitivity of sputum liquid culture testing (94%, 95% CI 0.88 to 0.98, P = 0.17).
The researchers conclude that “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.”
Source: Maunank Shah, Willy Ssengooba, Derek Armstrong, Lydia Nakiyingi, Molly Holshouser, Jerrold J. Ellner, Moses Joloba, Yukari C. Manabe, Susan E. Dorman. Comparative performance of urinary lipoarabinomannan assays and Xpert MTB/RIF in HIV-infected individuals. AIDS. 2014; 28; 1307-1314.
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