From the Guidelines
A tuberculin skin test result with a 7 mm area of induration is considered positive for individuals with certain high-risk conditions, such as those with HIV infection, recent close contact with persons with infectious TB, or those receiving immunosuppressive therapy, as their risk of developing active TB is significantly increased. According to the American Thoracic Society guidelines 1, the interpretation of tuberculin skin test results depends on the individual's risk factors for tuberculosis. For individuals at highest risk, including those with HIV infection, receiving immunosuppressive therapy, or with recent close contact with persons with infectious TB, a result of >5 mm of induration is considered positive. However, for other groups with increased risk, such as recent immigrants from high-prevalence countries, injection drug users, or those with certain clinical conditions like silicosis or diabetes mellitus, a result of >10 mm of induration is considered positive. Since a 7 mm result falls between these two thresholds, it is not explicitly defined as positive for all groups, but rather for those with the highest risk of developing active TB. Key factors that increase the risk of TB and may lead to a positive test result with a lower induration threshold include:
- HIV infection
- Recent close contact with persons with infectious TB
- Receiving immunosuppressive therapy
- Abnormal chest radiographs consistent with prior TB
- Certain clinical conditions such as silicosis, diabetes mellitus, or chronic renal failure. It is essential to consider these risk factors when interpreting tuberculin skin test results to ensure accurate diagnosis and treatment of latent tuberculosis infection 1.
From the Research
Patient Groups with Positive Tuberculin Skin Test Results
A tuberculin skin test result with a 7 mm area of induration is considered positive for certain patient groups, including:
- People living with HIV, as the cutoff value for a positive test result may be reduced to compensate for loss of sensitivity due to immunocompromisation 2
- Individuals with other medical conditions that may increase their risk of developing active tuberculosis, although the specific cutoff value for these groups is not specified in the provided studies
- Children and adults who are household contacts of pulmonary TB cases, as they are at high risk of latent tuberculosis infection (LTBI) 3
Cutoff Values for Positive Test Results
The cutoff values for positive tuberculin skin test results vary depending on the patient group, including:
- 10 mm or more for the general population
- 5 mm or more for people living with HIV and other immunocompromised individuals 2
- It is not clear from the provided studies whether a 7 mm induration would be considered positive for all patient groups, but it may be considered positive for certain high-risk groups, such as those with HIV infection or other medical conditions that increase their risk of developing active tuberculosis 2