Interpretation of the Purified Protein Derivative (PPD) Skin Test for Tuberculosis


I. An induration of 5 mm or more is classified as positive in the following:
  • Persons who have human immunodeficiency virus (HIV) infection or who have risk factors for HIV infection but unknown HIV status.
  • Persons who have had recent close contact with individuals who have active tuberculosis (recent close contact implies either household or social contact or unprotected occupational exposure similar in intensity and duration to household contact).
  • Persons who have fibrotic chest radiographs (consistent with healed tuberculosis).


    • II. An induration of 10 mm or more is classified as positive in all persons who do not meet any of the criteria in section I but
    who have other risk factors for tuberculosis, including the following:
  • High-risk groups
  • Injecting-drug users known to be HIV-seronegative
  • Persons who have other medical conditions that reportedly increase the risk of progressing from latent tuberculous infection to active tuberculosis: Silicosis, Gastrectomy or jejunoileal bypass, Body weight that is 10 percent or more below the ideal for age and height, Chronic renal failure with renal dialysis, Diabetes mellitus, High-dose corticosteroid or other immunosuppressive therapy, Some hematologic disorders, including malignancies such as leukemia and lymphoma, Other malignancies
  • Children less than four years old
  • High-prevalence groups
  • Persons born in Asian, African, Caribbean and Latin American countries with a high prevalence of tuberculosis
  • Persons from medically underserved, low-income populations
  • Residents of facilities providing long-term care, such as correctional institutions and nursing homes
  • Persons from high-risk populations in their communities, as determined by local public health authorities

    • III. An induration of 15 mm or more is classified as positive in persons who do not meet any of the criteria in sections I and II.

    IV Recent converters are defined on the basis of both the size of the induration and the age of the person being tested.
  • A 10-mm or greater increase in the induration size within a two-year period is classified as a recent conversion in persons younger than 35 years.
  • A 15-mm or greater increase in the induration size within a two-year period is classified as a recent conversion in persons 35 years of age and older.


    • V. PPD skin test results in health care workers:
  • In general, the recommendations in sections I, II and III should be followed when interpreting skin test results in health care workers.
  • The prevalence of tuberculosis in a facility should be considered when choosing the appropriate cutoff point for defining a positive PPD reaction. In facilities where the risk of exposure to Mycobacterium tuberculosis is minimal to very low, an induration of 15 mm or greater may be a suitable cutoff point for health care workers who have no other risk factors. In facilities where tuberculosis patients receive care, the cutoff point for health care workers with no other risk factors may be an induration of 10 mm or greater.
  • Generally, recent conversion of a PPD test from negative to positive in a health care worker should be defined as a 10-mm or greater increase in the induration size within a two-year period. For health care workers who are employed in facilities where tuberculosis exposure is very unlikely (e.g., minimal-risk facilities), an induration increase of 15 mm or more within a two-year period may be more appropriate for defining a recent conversion, because of the lower positive predictive value of the test in such groups.


    • Adapted from Guidelines for preventing the transmission of Mycobacterium tuberculosis in healthcare facilities.
    MMWR Morb Mortal Wkly Rep 1994;43(RR-13):1-132 as published in FEBRUARY 15, 1998 / VOLUME 57, NUMBER 4 AMERICAN FAMILY PHYSICIAN

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