What are the next steps and treatment options for individuals with positive or negative Purified Protein Derivative (PPD) test results?

Management of Positive and Negative PPD Test Results

For individuals with a positive PPD test result, the next step is a clinical evaluation and chest radiograph to rule out active tuberculosis, followed by appropriate treatment for latent tuberculosis infection if active disease is excluded. 1

Interpretation of PPD Results

PPD test results are interpreted based on the size of induration and risk factors:

• ≥5 mm induration is positive in:

  • HIV-infected persons
  • Recent contacts of TB cases
  • Persons with fibrotic changes on chest X-ray consistent with prior TB
  • Immunosuppressed patients 2, 3

• ≥10 mm induration is positive in:

  • Recent immigrants from high-prevalence areas
  • Injection drug users
  • Residents of congregate settings
  • Persons with certain medical conditions (diabetes, silicosis, etc.)
  • Children less than 4 years old 2, 3

• ≥15 mm induration is positive in:

  • Persons with no known risk factors 2, 4

Management Algorithm for PPD Results

For Negative PPD Results:

1. If the PPD is negative with a valid test, no further treatment is required 5
2. Consider the possibility of anergy in immunocompromised individuals
3. If high clinical suspicion despite negative PPD:
   • Obtain chest radiograph
   • If chest radiograph reveals scarring or a Ghon-like complex, monitor for opportunistic infections 5

For Positive PPD Results:

1. Immediate Clinical Evaluation:

   • Thorough symptom assessment (cough ≥2-3 weeks, fever, night sweats, weight loss, hemoptysis)
   • Chest radiograph 5, 1

2. If Active TB is Suspected:

   • Collect three sputum specimens for AFB smear microscopy and culture
   • Promptly initiate a four-drug regimen if clinical suspicion is high 5
   • Implement respiratory isolation until patient is no longer infectious (typically after 2-3 weeks of effective therapy) 2

3. If Active TB is Ruled Out (Latent TB Infection):

   • Determine appropriate preventive therapy based on risk factors:

     a) Standard regimen: Isoniazid (INH) 300 mg daily for adults for 9 months 5, 3, 1

     b) Alternative regimens:

     • Rifampin 600 mg daily for 4 months
     • Isoniazid plus rifampin for 3-4 months 2

   • Extended therapy (12 months) is recommended for:

     • HIV-infected persons
     • Persons with fibrotic pulmonary lesions consistent with healed TB
     • Persons with silicosis 3

4. Monitoring During Treatment:

   • Liver function tests every 2-4 weeks while receiving antituberculous treatment
   • Monitor for clinical symptoms of toxicity (nausea, vomiting, jaundice) 5, 2
   • Educate patients about symptoms of active TB and when to seek medical attention 2

Special Considerations

BCG Vaccination History

• Prior BCG vaccination can cause false-positive PPD results, but this effect diminishes with time
• In close contacts of active TB cases, a positive PPD should be considered indicative of TB infection regardless of BCG history 2
• Consider IGRA testing (QuantiFERON-TB Gold) as a confirmatory test in BCG-vaccinated individuals 2

High-Risk Populations

• Patients with HIV infection have higher rates of progression from latent to active TB
• Patients receiving immunosuppressive therapy (especially TNF blockers) require careful screening and prophylaxis before starting treatment 6
• Renal dialysis patients are at increased risk and should be screened with a designed prospective plan 7

Common Pitfalls to Avoid

1. Failing to report TB cases: All suspected or confirmed TB cases must be reported to the local health department 2

2. Unnecessary lateral chest radiographs: In pre-employment screening of individuals with positive PPD results, a single PA radiograph is sufficient; lateral views add no clinically relevant information 8

3. Inadequate treatment duration: Shorter treatment regimens may be insufficient, particularly for high-risk groups who require extended therapy 3

4. Overlooking drug toxicity: Regular monitoring of liver function and symptoms is essential during treatment 5

5. Misinterpreting boosted reactions: Two-step testing should be used when PPD testing is to be repeated periodically to avoid misinterpreting a boosted reaction as a new infection 5