Blood tests for diagnosis of tuberculosis.

摘要

Accurate diagnosis of tuberculosis has always been a problem. Mycobacterial culture, despite being the gold standard, is of limited value because of the long delay in getting the result and difficulties involved in culture.Giovanni Ferrara and colleagues (April 22, p 1328)1 assessed the interferon-gamma-based commercial blood tests T-SPOT.TB and QuantiFERON-TB Gold and showed that they had higher specificity than the tuberculin skin test. However, the tuberculin test will always have a value in settings where sensitivity matters more than specificity. In Ferrara and colleagues' analysis, figure 1 shows that the T-SPOT.TB test was negative in 41 patients (21-8%) whose tuberculin skin test was positive. Similarly, the QuantiFERON-TB Gold test was negative in 53 patients (26-8%) whose tuberculin skin test was positive. This finding means that the sensitivity of both tests is much lower than a tuberculin test done with 5 tuberculin units (TU) of purified protein derivative (PPD).