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QuantiFERON-TB Gold In-Tube

Applications and Keys to Accurate Performance



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Limitations of TST

Slide 4

November 2009

Although the tuberculin skin test has been used routinely for nearly a century, there are significant limitations associated with this test that I’d like to review. First, the tuberculin skin test requires trained personnel to accurately administer the purified protein derivative, and placement errors can cause erroneous results.

In addition, the test is subject to reader variability, and this subjective interpretation can lead to varying and inaccurate findings. The tuberculin skin test is also subject to something called the “boost” response, where an initial placement of PPD can enhance or boost subsequent TST reactions.

One of the major limitations of the tuberculin skin test is its low specificity, especially in individuals that have received the BCG vaccine, or in those that are infected with certain nontuberculous mycobacteria. The test can also demonstrate low sensitivity, and this is a problem in immunocompromised hosts. The final limitation that I’d like to emphasize is the low compliance rate for patients returning to have their skin test read 48 to 72 hours following placement. This requirement for a second visit has ultimately led to many patients being “lost to follow-up” without their TB status being determined, and this increases the risk of patients with LTBI going unidentified.

Due to the limitations associated with the tuberculin skin test, there’s been a significant amount of work over the past decade put into the development of new assays for the diagnosis of active and latent TB.

Limitations of TST

 


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