New TB Blood Test

Recently the Centers for Disease Control released new TB guidelines which allows medical practitioners to use a TB blood test called QuantiFERON-TB Gold, instead of the PPD, the traditional under-the-skin TB test.

Because the test is just a simple blood test, the person doesn’t have to come back to the doctor in 2-3 days to have the test read, which is more convenient. One other benefit reported by the experts is that the new TB blood test exhibits fewer false positives.

From a USA Today article- December 15, 2005

Certain non-tuberculosis bacteria can cause the skin test to yield a false-positive. People who have received a certain type of TB vaccine used in other countries are also prone to have false positives. People with AIDS or other immune deficiency conditions sometimes receive false negatives.

The new test is believed to be better at avoiding the false positives, Castro said. However, more study is needed, especially in use of the test on children and in people with compromised immune systems, CDC officials said.

“We’re saying this can be used instead of the tuberculin test. But we’re not going as far as saying it should replace it,” Castro said.

The QFT Gold test is made by an Australian company, and was approved by the FDA in May, 2005. Each QFT Gold test kit costs about $15, plus $10 or more to administer.

The skin test equipment is less expensive, but labor costs to get a result brings it to about the same price, said Dr. Masae Kawamura, director of the TB control section at the San Francisco health department.

The San Francisco health department started using the QFT Gold test in February, 2005, and now does most of its TB testing that way. It has led to large drops in positive readings, probably because the skin test was yielding false positives, Kawamura said. She said more accurate diagnoses could mean a reduction in health care costs.

“It really is a paradigm shift for those of us in TB control,” Kawamura said.

It will be interesting to see if this new test becomes the stadard of care across the US, especially in relationhip to the diagnosis of children.

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