Blood Test Believed Superior to Skin Test

Peter F. Barnes, M.D., of the Center for Pulmonary and Infectious Disease Control at the University of Texas Health Center in Tyler studied 413 individuals who have had contact with patients diagnosed with TB. After administering both tests to the group, the researchers found that the standard skin test returned positive results for exactly half of the subjects, while ELISPOT, the new blood test, only found TB in 39 percent.

The investigators argued that the blood test proved more accurate in TB diagnosis because it reduces the risk of error in test administration and interpretation, especially in developing nations. The authors also noted that certain types of vaccinations can trigger erroneous results from the skin test.

“Unfortunately, the standard method of diagnosing latent TB infection is the tuberculin skin test, which has many shortcomings,” said Dr. Barnes. “Two visits are required and skilled personnel are essential for proper placement and interpretation of the test. In addition, because purified protein derivative of tuberculin contains many antigens that are shared with other mycobacteria, the skin test does not reliably distinguish latent TB infection from prior immunization with bacilli Calmette-Guérin, or BCG vaccination, or from infection with environmental mycobacteria.”

“This is a major problem in most developed countries because a growing proportion of those with latent infection are foreign-born persons from high-incidence countries, most of whom received BCG vaccination during childhood,” Dr. Barnes continued. “A more accurate and convenient test to diagnosis latent TB infection would greatly enhance tuberculosis control efforts.”

COMPAMED.de; Source: American Thoracic Society (ATS)