PPD (purified protein derivative) or tuberculin is injected intradermally to test whether an individual is infected with tuberculosis. After 48-72 hours post-injection, the test is read by measuring:

PPD (purified protein derivative) or tuberculin is injected intradermally to test whether an individual is infected with tuberculosis. After 48-72 hours post-injection, the test is read by measuring:



A. The distance the bleb or wheal forms from the injection site
B. The diameter of the bleb or wheal
C. The number of blebs or wheals at the injection site
D. The intensity of the red coloration of the injection site


Answer: B. The diameter of the bleb or wheal


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