Urine test for TB marker not ready for routine use: review
The lipoarabinomannan urinary assay isn't accurate enough to be used for routine diagnosis of active tuberculosis.
The lipoarabinomannan (LAM) urinary assay isn't accurate enough to be used for routine diagnosis of active tuberculosis (TB), according to a review in the European Respiratory Journal.
Many had hoped that the Clearview TB ELISA (Inverness Medical Innovations/Alere) 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," wrote Dr. Dick Menzies of the Montreal Chest Institute and colleagues. Their paper appeared online July 4th.
The researchers pooled data from nine studies that compared LAM urine testing to 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 seven 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 cases as either positive or negative for TB.
The research team said the assay was more accurate in HIV-positive patients. In that group, its sensitivity for TB was 3% to 53% higher than in HIV-negative individuals, with similar specificity. Sensitivity was highest when immunosuppression was advanced, in which case there might be 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 wrote.
But they said this review shouldn't be the last word for the LAM assay.
"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 concluded, "as well as to assess newer versions of this test with technical advances compared to those reviewed here."
The manufacturer's representatives could not be reached for comment.
SOURCE: http://bit.ly/nPGeB9
Eur Respir J 2011.
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