Lateral Flow Urine Assay Detects TB In HIV+ Adults

Tuberculosis (TB) is a leading cause of death in human immunodeficiency virus (HIV)-positive people and conventional sputum tests for TB take time and are not always accurate in people with HIV.

A point-of-care test that does not depend on sputum evaluation, if sufficiently accurate, could help HIV-positive people who suffer high morbidity and mortality, by earlier detection of TB that may be missed by conventional sputum testing.

An international review team led by the those at the Liverpool School of Tropical Medicine (UK) have prepared a systematic review to assess the accuracy of a point-of-care urine test for diagnosing and screening for TB in people living with HIV infection. The review looked at accuracy of the lateral flow urine lipoarabinomannan assay (LF-LAM), a commercially available test that detects lipoarabinomannan (LAM), a component of mycobacterial cell walls, which is present in some people with active TB. The test is simple to carry out, requires no special equipment and provides a result within 25 minutes.

The review team examined all data published up until February 5, 2015 and included 12 studies. Six of the studies evaluated LF-LAM for TB diagnosis, looking at people with HIV and TB symptoms, while the other six evaluated the test for TB screening looking at people with HIV regardless of the presence of TB symptoms. The lateral flow urine lipoarabinomannan assay used in the studies was the Alere Determine TB LAM Ag, (Alere Inc.; Waltham, MA, USA), a commercially available point-of-care test for active pulmonary and extrapulmonary TB.

In HIV-positive people with TB symptoms, LF-LAM shows an average sensitivity and specificity of 45% and 92%. Based on these results, in 1,000 HIV-positive people where 30% (300 people) actually have TB, LF-FAM will identify 135 people with TB and miss the diagnosis in 165 with TB. For the 700 people who do not have TB, the test will correctly identify 644 people as not having TB, but will misclassify 56 as having TB. However, the sensitivity of the test is higher in HIV-positive individuals with low CD4 cell counts who are at risk of life-threatening illnesses. In patients with a CD4 less than 100 cells/µL, LF-LAM sensitivity was 56% versus 26% in patients with a CD4 count of more than 100 cells/µL.

Karen R. Steingart, MD, the senior author of the study said, “LF-LAM, whether used for diagnosis or screening, has low sensitivity to diagnose TB. However, and this is key, in HIV-positive individuals with low CD4 counts who are seriously ill, LF-LAM may help with the diagnosis of TB.” The study was published on May 10, 2016, in the journal Cochrane Database of Systematic Reviews.

Related Links:
Liverpool School of Tropical Medicine
Alere