NEW YORK (Reuters Health) – The lipoarabinomannan (LAM) urinary assay isn’t accurate enough to be used for routine TB diagnosis, according to a new review in the European Respiratory Journal.
That’s despite hope that the test, originally produced by Chemogen and now marketed by Inverness Medical Innovations as Clearview TB ELISA, could replace less convenient, non point-of-care TB testing.
The assay works by detecting the heat-stable glycolipid that is present in the cell walls of Mycobacterium tuberculosis and released from active or degrading cells during an infection.
“The LAM urine assay has many characteristics which make it a potentially useful rule-in TB diagnostic, but this review found inadequate sensitivity to use the LAM assay for the diagnosis of TB in unselected cohorts,” write researchers led by Dr. Dick Menzies of the Montreal Chest Institute.
Dr. Menzies and his colleagues pooled data from 9 studies that compared LAM urine testing against an accepted reference, such as positive culture or nucleic acid amplification for TB. Included were trials from Sweden, Ethiopia, Tanzania, Zimbabwe, South Africa, and India, with a total of close to 3,000 people.
In an analysis of 7 studies that only included microbiologically-confirmed cases of TB, LAM sensitivity ranged from 13% to 93%, and specificity was 87% to 99%.
Sensitivity also varied widely in two additional analyses that counted clinically-confirmed only cases as either positive or negative for TB.
The research team found that the assay was more accurate in detecting TB in HIV-positive patients, with sensitivity 3% to 53% higher compared to HIV-negative individuals, and a similar specificity. Sensitivity was highest in cases of advanced immunosuppression, which may lead to more LAM in the urine for detection.
“Despite very positive initial evaluations, larger and more recent studies have failed to demonstrate adequate sensitivity for TB diagnosis under routine conditions in unselected patients,” the authors write — but they say this review shouldn’t be the last word for LAM testing.
“Further studies are warranted to evaluate the added value of the LAM assay in the diagnosis of active TB in individuals with advanced HIV and in children,” they conclude, “as well as to assess newer versions of this test with technical advances compared to those reviewed here.”
European Respiratory Journal.