Test Improves Detection of Tuberculosis in HIV Patients

An international review team recently evaluated the accuracy of a point-of-care urine testing for the screening and diagnosis of tuberculosis (TB) in HIV patients.

Currently, sputum tests are in place to detect TB, but they take time and can produce inaccurate results in those living with HIV. However, the lateral flow urine lipoarabinomannan assay (LF-LAM) is a commercially available test that detects lipoarabinomannan (LAM), which is a component of the mycobacterial cell walls found in some patients with active TB.

The review looked at data published up until February 5, 2015, and included 12 studies, 6 of which evaluated LF-LAM for TB diagnosis in people with HIV and TB symptoms, and 6 that evaluated the test for TB screening with HIV patients regardless of whether they had symptoms of TB.

Researchers defined sensitivity as the percentage of patients whose tests were positive and diagnosed correctly, while specificity was defined as the percentage of patients correctly identified as not having the disease. Reviewers found that in HIV patients with TB symptoms, LF-LAM showed an average sensitivity of 45% and specificity of 92%.

Based on the results, in 1000 HIV patients where 30% have TB, LF-FAM can identify 135 people with TB and miss it in 165 people with TB. Additionally, for the 700 individuals who don’t have TB, the test will correctly identify 644 people who don’t have TB, but will misclassify 56 as having TB.

However, in HIV-positive patients with low CD4 cell counts who are at risk of developing life-threatening illnesses, the sensitivity of the test was higher. In patients with a CD4 ≤ 100 cells per µL, LF-LAM sensitivity was 56% versus 26% in patients with a CD4 count > 100 cells per µL.

“LF-LAM, whether used for diagnosis or screening, has low sensitivity to diagnose TB,” said senior review author Karen Steingart. “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 review findings should be interpreted with caution due to small number of studies and participants involved at this point.”