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Purified Protein Derivative (PPD): Sensitivity and Specificity

Introduction: None written. Excerpt from the entry in Tuberculosis:
adults with active TB

>=10mm threshold for induration

specificity in Japanese adults with a high rate of bCG vaccination. Note that non-TB mycobacterium (e.g. avium) also causes false positives: in US health care workers, in one study 50% of indurations 10-14mm were from M avium (PMID 11769770).

Some centers use a 'booster' or serial PPD strategy whereby a second PPD is placed 1-4 weeks after the first. The idea is to generate a stronger immune reaction in the second test, given that the reaction may be blunted if the initial TB exposure was long ago. This has not been evaluated for specificity.

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Associated Diagnoses:

Tuberculosis

90% sensitive, 35.4% specific