CDC: Aussies’ new TB assay looking good so far
Still needs more study, fine-tuning, experts add
Quantiferon, a new test that checks for TB infection by measuring blood levels of the cytokine interferon-gamma, may hit the U.S. market within the year, its Australian developers say. Though they’re still poring over results from a newly-completed, multi-site trial of Quantiferon, researchers at the Centers for Disease Control and Prevention in Atlanta agree that the trial data are looking good so far.
"Actually, I’m amazed by this test," says Jerry Mazurek, MD, the medical epidemiologist at the Division of TB Elimination at the CDC who oversaw the recent trials. "I think it’s a good test, and I wouldn’t be surprised if it proves to be a major contributor to improvement in TB control over the next decade or so."
Because it’s a lab test, one of Quantiferon’s advantages is that subjects don’t have to return for a reading. Instead, a 5 mm to 10 mm sample of whole blood is drawn and incubated over night with reagents, and results are available the following day. The test is already on the market in Australia and New Zealand, says Jim Rothel, PhD, an immunologist and spokesman for CSL Limited, the Australian biotechnology firm that developed the assay.
In the recently completed trials, Quantiferon showed generally good agreement with the Mantoux skin test, say Mazurek and Rothel.
"The two tests seem comparable, but there’s not 100% correlation," adds Rick O’Brien, MD, chief of research and evaluation at the CDC’s TB division.
"Plus, when there’s disagreement, we don’t yet know how to interpret it: Does that mean the skin test is wrong and Quantiferon is right? Or vice versa? So, more work still has to be done; there’s certainly some fine-tuning to do," O’Brien explains.
In Boston, one of the cities in which the test was put through its paces, the local TB controller gives Quantiferon high marks for general performance but has reservations about the test’s user-friendliness.
"Based on what I’ve seen, I like this test," says John Bernardo, MD, head of TB control in Boston. "I was impressed at the concordance between the [Mantoux] skin test and Quanti feron. And the fact that people won’t have to come back a second time to be read — that’s the big economy."
Plus, people from parts of the world where TB is endemic and/or where BCG is widely used don’t seem to balk at the idea of getting the blood test, Bernardo adds. "I think they view skin testing as sort of American-style nuisance, but they don’t harbor the same kinds of prejudice about taking a blood test."
Test may need more automation
As for user-friendliness, Bernardo says the jury’s still out as far he’s concerned. "It’s not an automated test," he explains. "You have to harvest the supernatants; you have to do an ELISA [enzyme-linked immunosorbent assay]. It’s not a big deal; still, I wonder if the test would be more consistent if it were a little more automated."
"Hmm. It’s a matter of perspective, I guess," counters Mazurek. "With this test, people will need to get used to the idea of relying on a lab test instead of a nurse."
Cost is still under consideration
Quantiferon could be on the market in the United States within the year, predicts Rothel, the CSL spokesman. The cost is still up in the air, he adds. "We’ve done calculations to try to see what the true per-unit cost of [a] skin test is, after you factor in staff time," he explains.
"We’re trying to keep our test on a par with that measure." That means a single test might retail here for somewhere in the neighborhood of $15, Rothel adds. "But please," he adds quickly, "don’t hold me to that."
O’Brien says he’s reserving judgment as to whether Quantiferon will land on American shelves anytime soon — or whether it will arrive here at all.
"I don’t know how our data will look once we’re finished with our analysis," he says. "And I’m not sure how the FDA will look at our data. It’s still too soon to say."
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