A low-cost assay that can be used in the clinic detected a proportion of advanced TB cases at an HIV center in South Africa. The researchers suggest using the test in areas with high TB prevalence might identify some people who would benefit from rapid anti-TB therapy.
TB is the most frequent complication of HIV infection in many parts of sub-Saharan Africa. Detecting and treating it earlier in HIV-positive people would have an impact on morbidity and mortality. A low-cost point-of-care urine assay for lipoarabinomannan (LAM) detects a certain proportion of TB cases in people starting antiretroviral therapy (ART). South African researchers conducted this study to see if LAM screening might prevent TB deaths in this population.
The study involved HIV-positive adults enrolling in a South African township ART clinic. All were screened for pulmonary TB by microscopy, liquid culture, and Xpert MTB/RIF using sputum samples. The researchers also retrospectively tested stored urine samples with the Determine TB-LAM assay, and these results were not used to inform treatment.
The study included 325 adults with a CD4 count below 200 cells/μL, 90 days of follow-up, and complete results. Fifty-nine of the 325 (18.2%) had culture-positive TB. Of these 59 people, 23 (39%) had a positive LAM result and 36 (61%) had a negative result.
Compared with LAM-negative people, those with LAM-positive TB had much lower CD4 counts, higher viral loads, lower hemoglobin, lower body mass index, and higher mycobacterial load. Compared with the LAM-negative group, the positive group was more often sputum smear positive and Xpert MTB/RIF positive, and they had a shorter time to sputum culture positivity.
Five of these 59 people died, 4 of them before TB treatment could begin. All 5 had a positive LAM test.
“A low-cost point-of-care urine test for LAM rapidly diagnoses a sub-group of cases with advanced HIV-associated TB and poor prognosis,” the researchers conclude.
If LAM were used with lab-based diagnostic assays, the researchers propose, “treatment delays would decrease and survival might be improved.”
Two of the investigators recently published a review on challenges facing use of the LAM assay, available at the link below.
Source: Stephen D. Lawn, Andrew D. Kerkhoff, Monica Vogt, Robin Wood. Clinical significance of lipoarabinomannan detection in urine using a low-cost point-of-care diagnostic assay for HIV-associated tuberculosis. AIDS. 2012; 26: 1635-1643.
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