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TB LAM: An Affordable Alternative to GeneXpert Testing for TB Among Patients with Advanced Immunosuppression or Who are Seriously Ill
Opportunistic infections (OIs) are infections that occur more often or are more severe in people with weakened immune systems, including people living with HIV (PLHIV). HIV damages the immune system, making it more difficult for the body to fight OIs. Tuberculosis (TB) is an OI; people infected with HIV are twenty to thirty times more likely to develop active TB and TB is the most common cause of death among PLHIV. Even though anti-retroviral therapy (ART) is widely available, many people with HIV infection who have access to HIV care still die with undiagnosed TB.
To address this situation, the WHO recommends that all PLHIV should be screened for TB at each clinical encounter. Early detection and initiation of treatment are essential to saving lives of PLHIV and preventing further spread of the disease to family members and other close contacts. Symptomatic patients (current cough, fever, weight loss or night sweats) should be tested and, if positive for TB, treated. Otherwise, they should be offered preventive therapy. WHO further recommends the use of a relatively new test, the Xpert MTB/RIF assay, which supports the rapid diagnosis of TB in about 2 hours as compared to several weeks with conventional sputum testing. To date, however, it has been difficult for many Ministries of Health to establish sustainable testing systems based on Xpert MTB/RIF testing because of the costs of the initial procurement of GeneXpert technology (about $32,000 for a four-cartridge machine) as well as the recurrent costs of testing supplies (about $9 per cartridge).
As the implementer of a regional project managed by the Centers for Disease Control (CDC), “HIV Co-infection Surveillance Strategies for Program Planning in the Central American Region under the President’s Emergency Plan for AIDS Relief (PEPFAR)”, University Research Co., LLC (URC) has seen the continued challenge of conducting a rapid TB test at HIV clinics that do not have on-site access to the Xpert MTB / RIF test. To help clinics in resource-poor countries find an affordable alternative to Xpert MTB/RIF assay testing, URC supported the use of a more affordable TB screening tool in patients with a compromised immune system (CD4 count <100 cells/ml) or who are seriously ill. In such patients, a urine specimen can be tested for the lipoarabinomannan (LAM) antigen to detect both pulmonary and extra-pulmonary TB. The test, known as TB LAM, is more sensitive than the conventional diagnostic tool (sputum smear microscopy) in HIV patients with compromised immune systems or who are seriously ill.
Six of my patients had a negative sputum smear result but tested positive with the TB LAM test. I’m very excited to say that these results allowed them to start the TB treatment, which helped to protect their families of TB transmission.
Dr Aura Marina Mendez, Medical Coordinator of the Escuintla HIV Clinic
URC supported the National TB Program in Guatemala to introduce TB LAM testing in July 2018 at an HIV clinic in the city of Escuintla. The intervention consisted of in-service training with both theoretical and practical components. First, clinic staff received orientation on TB diagnostic methods followed by a second, hands-on session in the laboratory focused on the TB LAM test and interpretation of results.
Between July and December 2018, 30 HIV patients with presumptive TB were tested with the conventional sputum smear test, which all came back negative. Sixteen patients in the cohort were eligible for TB LAM based on their immunosuppressed status or presentation of serious illness, six of whom tested positive for tuberculosis. On the same day, all six positive patients were referred for treatment to the TB clinic located at the same public health complex. Of those six patients, five eventually completed their TB treatment. Had those six patients not had access to TB LAM testing that day, they would have continued to be presumed TB negative. Not only could this have harmed their long-term health by allowing TB disease to advance further without treatment, it also would have put their family, community, and even medical workers at risk for TB infection.
At only about one-tenth the cost of the Xpert MTB/RIF test, TB LAM costs are comparable to those of the conventional sputum smear test, but with higher effectiveness for TB diagnosis in HIV cases. For countries that cannot yet afford to introduce GeneXpert testing in all HIV clinics, TB LAM can be successfully used to increase TB diagnosis and same-day treatment initiation among immunosuppressed patients.