Clinical significance of lipoarabinomannan detection in urine using a low-cost point-of-care diagnostic assay for HIV-associated tuberculosis

Abstract

Objective: A low-cost point-of-care urine assay for lipoarabinomannan (LAM) used for screening patients prior to antiretroviral therapy (ART) rapidly diagnoses a proportion of tuberculosis (TB) cases. We determined the characteristics and outcomes of such patients.

Methods: Adults enrolling in a South African township ART clinic were systematically screened for pulmonary TB by testing paired sputum samples using microscopy, liquid culture and Xpert MTB/RIF in a centralized laboratory. Stored urine samples were retrospectively tested for LAM using the Determine TB-LAM assay, but results did not inform treatment. Patients were followed up in the routine ART service and early (90-day) programmatic outcomes were determined. Analysis was restricted to those with CD4 cell counts below 200 cells/μl.

Results: Of patients with CD4 cell counts below 200 cells/μl and complete results (n=325), 59 (18.2%) had culture-positive TB. Of these, 23 (39%) patients tested urine LAM-positive and 36 (61%) urine LAM-negative. Patients with LAM-positive TB had much lower CD4 cell counts, higher plasma viral loads, lower haemoglobin concentrations and lower BMIs compared to those with LAM-negative TB. They also had evidence of higher mycobacterial load, more frequently testing sputum smear-positive, Xpert-positive (sputum and urine) and having a shorter time to sputum culture positivity. Of five (8.5%) patients who died, four did so before TB treatment was started. All five retrospectively tested LAM-positive.

Conclusions: 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. If used in combination with laboratory-based diagnostics, treatment delays would decrease and survival might be improved.