Urine Test for Tuberculosis Needs Improving

A noninvasive urinary assay for tuberculosis (TB) is not accurate enough to be used for routine diagnosis of active tuberculosis.

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.

A meta-analysis of and systematic review was conducted on the use of the lipoarabinomannan (LAM) urinary assay for the diagnosis of active TB. Scientists 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 team stated 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.

Dick Menzies, MD, a lead author of the study from the Montreal Chest Clinic (Montreal, QC, Canada), said, "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." However, further studies are warranted to evaluate the added value of the LAM assay, known as Clearview TB ELISA (Inverness Medical Innovations; Princeton, NJ, USA) in the diagnosis of active TB. It is especially important for individuals with advanced HIV and in children as well as to assess newer versions of this test with technical advances compared to those in the study. The review was published online on July 4, 2011, in the European Respiratory Journal.

Related Links:
Montreal Chest Clinic
Inverness Medical Innovations