Tuesday, November 30, 2021
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WHO issues guidance on LAM use in diagnosis of TB

The World Health Organisation (WHO) has updated its guidance for the use of lateral flow urine lipoarabinomannan assay (LAM) in the diagnosis of tuberculosis (TB). Following new evidence, WHO now recommends more broader use of urinary LAM assays for diagnosis of TB in people living with HIV.

“As we accelerate efforts to reach 40m people with TB care by 2022 as per the UN high-level meeting political declaration, we need to have more sensitive tools to diagnose TB in all patients, including in those with smear-negative TB, children and people living with HIV”, said Dr Tereza Kasaeva, director of the WHO Global TB Programme.

Tests based on the detection of mycobacterial LAM antigen in urine have emerged as potential point-of-care tests for TB. The WHO Global TB Programme recommended the use of LF-LAM for the first time in 2015. Urinary LAM assays have shown greater sensitivity (when used for the diagnosis of TB in people living with HIV. The sensitivity increases significantly in patients with lower CD4 cell counts. Following the new evidence, WHO is now recommending LF-LAM use to assist in diagnosis in a broader group of people, both in inpatient and outpatient settings.

In inpatient settings, WHO strongly recommends using LF-LAM to assist in the diagnosis of active TB in HIV-positive adults, adolescents and children with signs and symptoms of TB (pulmonary and/or extrapulmonary), or with advanced HIV disease (1) or who are seriously ill (2) or else irrespective of signs and symptoms of TB and with a CD4 cell count of less than 200 cells/mm3.

In outpatient settings, WHO suggests using LF-LAM to assist in the diagnosis of active TB in HIV-positive adults, adolescents and children: with signs and symptoms of TB (pulmonary and/or extrapulmonary) or seriously ill; or else irrespective of signs and symptoms of TB and with a CD4 cell count of less than 100 cells/mm3.

In outpatient settings, WHO recommends against using LF-LAM to assist in the diagnosis of active TB in HIV-positive adults, adolescents and children without assessing TB symptoms; or without TB symptoms and unknown CD4 cell count; or else without TB symptoms and CD4 cell count greater than or equal to 100 cells/mm3.

The WHO End TB Strategy prioritises early diagnosis of TB. This includes cases of smear-negative disease, which are often associated with HIV coinfection and young age. An estimated 9% (0.9 million) of the 10 million people who developed TB worldwide in 2018 were among people living with HIV. The vast majority of them (71%) are in the WHO African Region.

Notes:
(1) For adults, adolescents, and children aged 5 years or more, “advanced HIV disease” is defined as a CD4 cell count of less than 200 cells/mm3 or a WHO clinical stage 3 or 4 event at presentation for care. All children with HIV aged under 5 years should be considered as having advanced disease at presentation.
(2) “Seriously ill” is defined based on four danger signs: respiratory rate of more than 30/minute, temperature of more than 39 °C, heart rate of more than 120/minute and unable to walk unaided.

[link url="https://mailchi.mp/who/who_guidance_lf-lam_plhiv-update?e=5b995e9d69"]WHO guidance[/link]

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