PPD Skin Test

A PPD (purified protein derivative) intermediate skin test consists of 0.1 ml (5 tuberculin units) of PPD intradermally, usually on the volar surface of the forearm and read at 48 to 72 hours, recording the size of induration, not redness.

This test is not 100% sensitive for mycobacterium tuberculosis infection. Positive reactions also occur in patients who have received BCG (Bacillus of Calmette and Guerin) vaccination in the past as is often seen in patients from countries with a high incidence of TB infections.

Infections with atypical Mycobacteria (e.g. Mycobacterium avium complex (MAC) often seen in AIDS and/or HIV positive patients) can also result in a reaction to PPD.

Immunosuppressed patients (anergic), on the other hand, may have a negative PPD even though they have active TB or were infected with TB in the past.

In addition 10 to 20% of non-immunosuppressed patients, particularly those who are poorly nourished and/or protein-depleted, may have a negative PPD, even though they have active TB or were infected with TB in the past.





Return to What Is Tuberculosis

Return from PPD Skin Test to Medical Exam Essentials homepage

Don’t Miss
A Primer in Adult
Physical Diagnosis

With a 30-Day Money Back Guarantee, there is no risk involved in trying this handy new eBook.

Download the PDF now and start mastering the skills necessary for Physical Diagnosis.


Sign up for Periodic Site Updates

Add your name and e-mail address, and we’ll send you periodic site updates when we add other valuable documents for Medical Students.