Challenges in interpreting the urinary lipoarabinomannan test in patients with mycobacterial infections

Abstract

Background. Detection of lipoarabinomannan (LAM) in urine is recommended for the diagnosis of tuberculosis (TB) in HIV patients with a CD4 level below 200 c/µl. Theoretically, a false positive result due to nontuberculous mycobacteria is justified, but in the literature we find a small number of cases. Objective(s). Description of the causes of false positive results of the urinary LAM test in patients suspected of pulmonary TB and highlighting cross-reactivity with nontuberculous mycobacteria. Materials and methods. The case of a patient hospitalized in the IMSP SCM of Phthisiopneumology in Chisinau, Moldova, living with HIV with a CD4 level below 200 c/µl, with a false positive urinary LAM test and a latter appearance of positive cultures for Mycobacteria Avium was analyzed, and a narrative review of the literature on this subject was performed. Results. The case of a woman with HIV, CD4-24 c/µl. She presents with cough, fever, and chest X-ray with pulmonary condensation without improvement on antibiotic therapy. To exclude tuberculosis, sputum, bronchoalveolar lavage (BAL), urine and feces were collected, all of which was negative for AFB and Xpert MTB/RIf microscopy. At the same time, the urine LAM test was positive, justifying the initiation of antituberculosis treatment. On the 10th day of treatment, MGIT cultures from sputum and BAL were positive for M. avium. The diagnosis of pulmonary mycobacteriosis due to M. avium was established and the treatment was adjusted. Conclusion(s). Pulmonary mycobacteriosis caused by M. avium can cause false-positive results of the urinary LAM test, which creates diagnostic and therapeutic dilemmas in patients living with HIV which have a CD4 level below 200 c/µl, for whom the urinary LAM test has a high specificity.