New rapid test significantly more effective for TB-diagnosis in people with HIV

A new study has shown a new point-of-care (POC) device to diagnose tuberculosis (TB) in people living with HIV to be substantially (28%) more effective at identifying TB-positive patients than the only POC TB diagnostic device currently available, Alere Determine TB LAM Ag (AlereLAM).

The new Fujifilm SILVAMP TB LAM (FujiLAM) device was shown to be more sensitive than the current POC TB test, at 70.4% compared to 42.3%. This means that FujiLAM has the potential to reduce the number of false negative test results (where someone who has TB incorrectly tests negative). The specificity of the two tests, which measures the likelihood of a test returning a false negative result, was comparable at 90.8% for FujiLAM and 95% for AlereLAM.

There is an urgent need for more rapid, point-of-care diagnostic devises for TB. The challenge is especially important for people living with HIV, because sputum-based tests (which detect TB in saliva and mucous) have consistently demonstrated suboptimal results for immunocompromised individuals.

People living with HIV often have extrapulmonary TB, where the infection has affected parts of the body other than the lungs. This is difficult to diagnose with sputum alone, and severely immunocompromised individuals may have trouble producing the sputum needed for a sample.

Instead of using sputum, both FujiLAM and AlereLAM test for TB in samples of urine, detecting lipoarabinomannan a component of a bacterium found in urine and indicative of TB infection. This present study was conducted to assess the diagnostic accuracy of FujiLAM for the detection of active tuberculosis compared with AlereLAM in hospital patients with HIV.

968 patients from three separate cohorts of hospital in-patients living with HIV in South Africa were included in the final analysis. 62% of the patients were later defined as having active TB, 9% were defined as unknown, and 29% were defined as non-TB.

The median patient age was 35, and the median CD4 count was 113 cells per copy in cohort 1, 153 cells per copy in cohort 2 and 59 cells per copy in cohort 3. Just under half (45%) had a previous history of TB. Cohort 3, which had more people with advanced HIV disease than other cohorts, had the highest sensitivity result at 81% compared to the microbiological reference standard.

Among all patients with a CD4 count less than 100 cells per copy, FujiLAM had a sensitivity of 84.2% compared with 57.3% for AlereLAM. Among patients with CD4 counts over 200 cells per copy, sensitivity was 44% and 12.2% respectively.

The findings are backed up by a previous systematic review carried out by the World Health Organization, which found similar sensitivity and specificity results for the AlereLAM device. The authors conclude that the FujiLAM point-of-care assay could save lives by enabling earlier diagnosis of HIV-associated TB in more inpatients than AlereLAM. But before it can be implemented into clinical practice, further research is warranted and outside of a research laboratory setting.

Authors of the present study led by Tobias Broger and Bianca Sossen, comment, “since AlereLAM has demonstrated survival benefit, FujiLAM might potentially further reduce tuberculosis-related mortality in people with HIV.”

“These findings will inform a WHO policy review for lipoarabinomannan-based diagnostic tests of active tuberculosis. Further research, including prospective and operational studies on the FujiLAM assay in settings of intended use and in additional patient populations, including outpatients with HIV, populations without HIV, and paediatric populations, are needed.”