More Accurate TB Blood Tests Replacing Old Skin Testing at VA

by U.S. Medicine

May 15, 2012

By Rachel Pomerance

PALO ALTO, CA — As a physician with Stanford University’s emergency department and occupational health center, Wendy Thanassi, MD, got an early look at usage of Interferon-Gamma Release Assays (IGRA), revolutionary new blood tests that screen for tuberculosis.


– Wendy Thanassi, MD

So in 2009, when she became chief of occupational services at the VA Palo Alto Health Care System, Thanassi advised supplanting the traditional tuberculin skin test (TST) with the third-generation QuantiFERON test, known as QuantiFERON-TB Gold In-Tube (QFT-GIT). It is one of two types of IGRA available for use at VA; the other is the T-SPOT.TB test, which became available on the Federal Supply Schedule for Medical Laboratory Testing and Analysis Services in November.

“We all knew that [IGRAs] are a better test than the TST. We knew that it would provide us more accurate information,” Thanassi said, praising her director’s office for jumping on the opportunity to pursue the first advancement in TB testing in more than a century.

Now that the Palo Alto VA has administered 15,000 of the blood tests, Thanassi has the data to back up a move she called “absolutely invaluable.”

Results such as hers have the VA gearing up for a transition to TB testing through the blood tests and weighing the advantages of each type. Available IGRAs include the QuantiFERON tests (QFT), which can be handled by an internal lab, and the T-SPOT.TB, which requires considerably less blood and is more sensitive in certain situations but must be sent away for results. Both are considered far more efficient than the skin tests, notorious for inconsistencies in patient compliance and clinical interpretation as well as false positives for those vaccinated for tuberculosis.

Earlier this year, Under Secretary of Health Robert Petzel, MD,  dispatched a letter on the subject to the publication distribution list of the Veterans Health Administration.

“IGRAs are cost-effective tests that can be used in place of TSTs in all situations in which the CDC recommends TST,” Petzel stated. “Further head-to-head comparison studies need to be performed to determine if one IGRA is more sensitive or specific than another.”

 

TB Chart

More Accurate TB Blood Tests Replacing Old Skin Testing at VA Cont

Petzel also issued the following caveat: “Prior to implementing IGRAs, it is suggested that individual facilities determine test availability and overall costs and benefits of testing. It is recommended that consideration be given to having specific days to collect and process the IGRA samples to ensure appropriate collection procedures, adequate laboratory support and accurate test results.”

In the case of the Palo Alto VA, testing via QFT-GIT indicated that previous tests vastly overestimated the number of infected employees. While skin tests indicated that about 40% of the employee population suffered from latent TB, blood testing found only 7% of employees with the condition.


Skin tests for tuberculosis are notorious for inconsistencies in patient compliance and clinical interpretation as well as producing false positives for those vaccinated for TB.

“What that does is it saves the employees and the institutions an incredible amount of time and money,” Thanassi said. In the old model, everyone who had been diagnosed with a false positive would have required chest X-rays and “might have been treated for TB with a relatively toxic regimen of nine months of therapy” that carried such side effects as “significant liver toxicity and failure.”

The VA Central Office has awarded Thanassi a two-year grant to consider recommendations for using IGRAs to test the VA’s national network of 420,000 employees and volunteers. 

On the East Coast, Sally Foster-Chang, a nurse practitioner with the Philadelphia VA Medical Center, is working with the VA Central Office on a business plan examining the cost savings of the T-SPOT.

The potential savings of time and money inspired Foster-Chang to delve deeply into the subject. When she met Thanassi at a federal occupational health conference, Foster-Chang determined that IGRAs could save the Philadelphia VA Medical Center 1,300 hours of clinical time and $136,000 per year.

“From my own perspective as an occupational health provider, one of the best advantages of the IGRIs is that it only requires one visit,” Foster-Chang said. The follow-up appointments required to read skin test results mean additional work for the clinician and time away from work for the VA employee, she said. Plus, since 15% to 20% of people fail to make the follow-up visit, more time and money are lost to tracking people down and repeating tests. “I think one program shouldn’t take over one-quarter of our clinical time,” she said. “For the last two years, we’ve been more or less hogtied by the time demands of the tuberculosis screening program.”

Foster-Chang is considering the T-SPOT test in part because it requires one tube of blood as opposed to three needed for the QFT and due to its accuracy in testing those with immune deficiencies, where TB is a common opportunistic infection.

“I think we need to all think about doing some preliminary studies in our specific situations” before determining which tests to adopt,” Foster-Chang said.

Considerable education is needed to prepare clinicians to use these tests and interpret their borderline zones, she added. Still, Thanassi called their adoption “inevitable,” especially in the coastal and southern United States with the highest incidences of tuberculosis.

“Every clinician strives for accuracy,” she said, and “we all want the best test for our patients.” According to Thanassi, IGRAs are that test for TB – and marking “the first time in 130 years that we have a diagnostic test that we can believe.”

While TB is currently less of a threat in this country, “worldwide, it is still the biggest killer as far as infectious diseases go,” said Chuck Sohaskey, PhD, with the Tuberculosis Research Lab of the VA Long Beach Healthcare System (CA).”

“What we need to remember is this is a disease of incredible global burden,” Thanassi said, and the use of these tests “changes the world.”

Back to 2012 Compendium


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