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Experts: Blood test a more efficient, cheaper way spot tuberculosis

While the legacy skin test is cheaper in terms of materials, it requires more staff time, and a greater commitment on the part of the patient.

Jeff Lagasse, Associate Editor

As hospitals look to trim costs, experts say that blood testing for tuberculosis, as opposed to skin testing, can result in big savings despite the higher up-front costs associated with the practice.

William Cruikshank, PhD at Oxford Immunotec, said that tuberculin skin test, or TST, relies on a different set of cells to indicate a positive response. The blood test, known as the interferon-y release assay, or IGRA, is more efficient, he said.

"In the old-fashioned skin test, they give you different components of the bacteria under the skin," said Cruikshank. "You develop an immune response with memory cells recognizing there's more bacteria in the system. That generates an inflammatory response at the site of infection, and we measure that to see how severe the response was.

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"IGRA is a more rapid response," he said. "It relies on affector cells, seeing if they respond to the components of the bacteria. If you do get a response, that means you have been exposed to tuberculosis."

That rapid response is the key to IGRA's potential for cost savings. While the TST test is actually cheaper in terms of materials, it requires more staff time, and a greater commitment on the part of the patient -- meaning there's greater potential for something to go wrong during the process, possibly resulting in a re-test or, worse, a false positive.

"The skin test is 38 to 40 cents -- it's very cheap," said Edward Bernacki, MD, a professor at the University of Texas-Austin and a Johns Hopkins University faculty member. "The problem is the expense to administer it. You need a nurse practitioner, or a nurse who's trained in doing this, to apply this to the skin … to get the proper reaction. So you need a trained individual, and you need the person who's being assessed to come back again and have the test read in 48 to 72 hours. There's a lot of labor involved in the process."

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Chris Bos, director of human resources and employee health at Mercy Health Springfield Communities in Missouri, said results from the IGRA test typically take 48 hours at most. The blood is drawn, shipped to the lab, and results can be checked on an online portal as soon as they're available.

Under the TST framework, initial results could be read between 48 to 72 hours after administration, but that would be the beginning of a process of follow-up appointments and re-testing that could last as long as 13 days, said Bos.

"Inevitably, the person would forget to come back in, or forget to get placement," he said. "There's a lot of areas where things could go wrong."

Factoring in the cost of supplies, the skin test is about $13, said Bos -- compared to about $50 for the IGRA blood test. But the labor costs associated with TST are not only high, but frequently underexamined. Bernacki said that's why many hospitals have yet to make the switch, particularly when it comes to testing their own employees.

"It's an inexpensive modality," said Bernacki. "Many institutions haven't really thought about those trade-offs. There's a lot of hidden costs in doing things. … The labor costs are so high that if you have to take an hour, two hours out of people's day to come to occupational health to have it read, that's a lot of time. You're talking about someone who makes $20 to $30 an hour just hanging around."

Bernacki's institution has been using the IGRA test for years now, and finds that it's especially useful when testing foreign-born individuals, who he said traditionally have a higher rate of tuberculosis.

And it doesn't take much to make the switch from TST to IGRA, he said; contracting with the company that does the test is about the only real commitment required.

Bos said comfort is another reason why some hospitals haven't yet made the switch.

"It's been around since 1977, so they don't remember a time when it wasn't a skin test," he said.

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The only concern with the blood test, said Bos, is that on rare occasions the sample won't get shipped to the testing facility in time, which usually happens due to bad weather. But that's only happened twice in the past year, he said, with the biggest inconvenience being the need for a patient to come back in and have another sample drawn.

Cindy Callahan, a nurse at Oxford Immunotec who has studied TB screening costs at several hospitals throughout the country, recently spent two weeks at Johns Hopkins studying the most cost effective ways to conduct tuberculosis testing. Not only did the IGRA test result in greater savings in labor and allocation of resources, but there was much higher compliance when it came to employees' annual testing, which is required by the joint commission.

"We would do all these cost analyses, and it would show phenomenal cost savings, and staff time," she said. "It's not just about the hard costs. It's not that much more money."

Twitter: @JELagasse

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