What is the next step after a positive Purified Protein Derivative (PPD) test result?

Next Steps After a Positive PPD Test

After a positive Purified Protein Derivative (PPD) test, the immediate next step is to perform a clinical examination and chest radiograph to rule out active tuberculosis. 1

Initial Evaluation

• All individuals with newly recognized positive PPD test results should be promptly evaluated for active tuberculosis through a clinical examination and chest radiograph 1
• If the history, clinical examination, or chest radiograph is compatible with active TB, additional diagnostic tests should be performed, including sputum examination for acid-fast bacilli (AFB) 1
• If symptoms compatible with TB are present (persistent cough lasting ≥3 weeks, bloody sputum, night sweats, weight loss, anorexia, or fever), the individual should be excluded from workplace/normal activities until active TB is ruled out or treatment is initiated 1

Interpretation of Positive PPD Results

The definition of a positive PPD test varies based on risk factors:

• ≥5 mm induration is considered positive for:

  • Persons with HIV infection or at risk for HIV infection 1, 2
  • Recent contacts of persons with infectious TB 2, 3
  • Persons with fibrotic changes on chest radiograph consistent with prior TB 2

• ≥10 mm induration is considered positive for:

  • Recent converters (≥10 mm increase within 2 years for those <35 years old) 2
  • Intravenous drug users known to be HIV-negative 2
  • Persons with certain medical conditions (diabetes, silicosis, immunosuppressive therapy, etc.) 2
  • Foreign-born persons from high-prevalence countries 2
  • Residents of long-term care facilities 2
  • Children less than 4 years old 2

• ≥15 mm induration is considered positive for persons with no known risk factors 2, 3

Management Based on Evaluation Results

If Active TB is Ruled Out:

• Evaluate for preventive therapy (treatment of latent TB infection) according to published guidelines 1
• Candidates for preventive therapy include:
  • Persons under age 35 with recent conversion (≥10 mm induration) 2, 3
  • Persons over age 35 with ≥15 mm induration 3
  • Persons with HIV infection (regardless of age) 2
  • Persons with radiographic evidence of previous TB 2
  • Persons with certain medical conditions that increase TB risk 2

Preventive Therapy Regimens:

• Standard regimen: Isoniazid (INH) 300 mg daily for adults and 10 mg/kg/day for children 1
• Duration of therapy:
  • 9 months for most individuals 4
  • 12 months for HIV-infected persons and those with radiographic evidence of previous TB 1, 2, 3
• Alternative regimen: 4 months of rifampin (600 mg/day) for those who cannot tolerate INH or are exposed to INH-resistant organisms 1
• For those with silicosis or fibrotic lesions: 12 months of INH or 4 months of INH plus rifampin 1, 2

Monitoring During Preventive Therapy:

• Monthly assessment for adverse reactions, particularly hepatotoxicity 1
• For persons over 35 years of age, obtain baseline transaminase measurements and monitor monthly 1
• Educate patients about potential adverse effects, particularly signs of hepatitis (nausea, vomiting, jaundice) 1

If Active TB is Diagnosed:

• Initiate appropriate multi-drug therapy according to susceptibility patterns 1
• Exclude from workplace/normal activities until non-infectious 1
• Document adequate therapy, resolution of cough, and three consecutive negative sputum smears before return to normal activities 1

Special Considerations

• For healthcare workers (HCWs), document the positive PPD result in their health record and determine if it represents a conversion from a previous negative test 1
• If conversion has occurred, investigate potential sources of exposure 1
• For persons with BCG vaccination history, a PPD reaction ≥10 mm is likely due to TB infection rather than BCG, especially if vaccination was in childhood and the person is from a high TB prevalence country 1
• For immunocompromised individuals, consider more frequent monitoring for TB symptoms even after preventive therapy 1

Common Pitfalls to Avoid

• Do not rely on patient self-reading of PPD results; tests should be read by trained personnel 48-72 hours after administration 1
• Do not mistake a boosted reaction for a true conversion; use two-step testing for baseline assessment when indicated 1
• Do not assume that BCG vaccination is the cause of a positive PPD, especially in persons from high TB prevalence areas 1
• Do not overlook the possibility of anergy in HIV-infected or severely immunocompromised individuals, which may lead to false-negative PPD results 5
• Do not routinely repeat chest radiographs in asymptomatic individuals with normal initial radiographs 1