Tuberculosis screening
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Overview
Screening for tuberculosis is generally done with using a mantoux tuberculin skin test, also known as a tuberculin skin test or a PPD. The test involves injecting a small amount of a purified protein derivative of the tuberculosis bacterium intradermally, and watching for a reaction in the following days.
Screening
The results of a Mantoux tuberculin skin test must be interpreted carefully. The person's medical risk factors determine at which increment (5 mm, 10 mm, or 15 mm) of induration the result is considered positive.[1] A positive result indicates TB exposure.
- 5 mm or more is positive in
- HIV-positive person
- Recent contacts of TB case
- Persons with nodular or fibrotic changes on chest x-ray consistent with old healed TB
- Patients with organ transplants and other immunosuppressed patients
- 10 mm or more is positive in
- Recent arrivals (less than 5 years) from high-prevalence countries
- Injection drug users
- Residents and employees of high-risk congregate settings (e.g., prisons, nursing homes, hospitals, homeless shelters, etc.)
- Mycobacteriology lab personnel
- Persons with clinical conditions that place them at high risk (e.g., diabetes, prolonged corticosteroid therapy, leukemia, end-stage renal disease, chronic malabsorption syndromes, low body weight, etc)
- Children less than 4 years of age, or children and adolescents exposed to adults in high-risk categories
- 15 mm or more is positive in
- Persons with no known risk factors for TB
- (Note: Targeted skin testing programs should only be conducted among high-risk groups)
A few important notes about Mantoux tuberculin skin tests:
- A tuberculin test conversion is defined as an increase of 10 mm or more within a 2-year period, regardless of age.
- Mycobacterium avium intracellulare (MAI) or other mycobacterium cause 5 mm induration, but TB is what causes ≥10mm.
- Decision to test is decision to treat.
- If a patient is treated fully, then re-exposed, they should only be retreated if they are HIV positive (immunocompromised) or the risk of reinfection is high.
Contact Screening
When someone is diagnosed with tuberculosis, all their close contacts should be screened for TB with a tuberculin skin test or a chest x-ray or both.
References
- ↑ From the CDC team of the CDC team at the Saskatchewan Lung Association, photos of a PPD bump.