CDC recommends new blood test for TB

Seattle Post-Intelligencer ^ | December 15, 2005 | MIKE STOBBE

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ASSOCIATED PRESS

ATLANTA -- Federal health officials are recommending a new, more accurate blood test for tuberculosis that may someday replace the skin test used for the past 100 years.

The Centers for Disease Control and Prevention said Thursday that the test - called the QuantiFERON-TB Gold - is less likely to yield false positive readings and more convenient for patients.

"This is one of the first TB advancements made since the discovery of antibiotics. ... This is a huge deal," said Jennifer Grinsdale, an epidemiologist with the San Francisco Department of Public Health.

With the skin test, a health care worker injects a small amount of protein-bearing testing fluid - called tuberculin - just under the skin on the underside of the forearm. After two or three days, the patient must return so that the health care worker can assess the swelling and decide if the test is positive or not.

With the QFT Gold test, the patient must come in only once, to have some blood drawn. The patient is then notified when the results become available, which can be as soon as the next day.

It also seems to address gripes health officials have had with the skin test.

"I like to refer to the tuberculin skin test as the test we love to hate," said Dr. Kenneth Castro, director of the CDC's Division of Tuberculosis Elimination.

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, Cellestis Limited. The U.S. Food and Drug Administration approved the product in May.

An earlier version of the QFT test was recommended by the CDC, but with restrictions on which types of cases it should be used in.

It was not considered much more accurate than the skin test and it was not well received by most local health departments, said Dr. Neil Schluger, an associate professor of medicine and public health at Columbia University who chaired a CDC advisory committee that reviewed the QFT Gold test.

Each QFT Gold test kit costs about $15, and an additional $10 or so 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, 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.