Latent Tuberculosis Infection Diagnosis and Management

Diagnostic Criteria

• A positive Tuberculin Skin Test (TST) result is defined as induration ≥5 mm in high-risk individuals, as recommended by the American Gastroenterological Association 1
• The TST measures delayed-type hypersensitivity response to purified protein derivative (PPD) and may be falsely positive in BCG-vaccinated individuals or falsely negative in patients on immunosuppressive therapy, including corticosteroids, thiopurines, or methotrexate, according to the American Gastroenterological Association 1

Screening and Testing

• Initial screening should include patient history, chest X-ray, and TST and/or Interferon-Gamma Release Assays (IGRAs), as recommended by the American Gastroenterological Association 1
• HIV-infected patients should be tested at initiation of care, and repeat testing is recommended if initial result is negative but CD4 count increases to >200 cells/μL after starting antiretroviral therapy, according to the Infectious Diseases Society of America 2
• Close contacts of infectious TB should be treated for LTBI regardless of TST/IGRA results, as recommended by the Infectious Diseases Society of America 2 and supported by the Centers for Disease Control and Prevention (CDC) and the American Thoracic Society (ATS) 2

Special Populations

• Patients starting anti-TNF therapy should undergo mandatory screening before initiating therapy, and IGRA is preferred in BCG-vaccinated individuals, as recommended by the American Gastroenterological Association 1 and the European Crohn's and Colitis Organisation 1, 3
• Complete treatment of LTBI is required before starting anti-TNF therapy, as recommended by the European Crohn's and Colitis Organisation 1
• Pregnant women with LTBI should receive 9 months of isoniazid, with a maximum protective effect of over 90% if completed properly (strong recommendation, moderate quality evidence) 4, 5, 6, 7
• Children under 5 years have a higher risk of progression to active TB if untreated, making treatment particularly important (strong recommendation, moderate quality evidence) 8

Treatment Regimens

Monitoring and Follow-up

• The CDC recommends periodic evaluation (intervals <6 months) to detect symptoms of active TB, and education on symptoms of TB (cough with or without fever, night sweats, weight loss) is recommended 9
• Baseline liver function tests are only recommended for children with risk factors, and pyridoxine (vitamin B6) supplementation is recommended for certain children (strong recommendation, moderate quality evidence) 6, 10, 4, 5
• Inadequate monitoring for hepatotoxicity, particularly with isoniazid regimens, can lead to adverse effects, and overlooking drug interactions with rifampin-containing regimens can lead to adverse effects (strong recommendation, moderate quality evidence) 4, 11

Common Pitfalls and Considerations

• Misinterpreting false-negative TST results in immunosuppressed patients can lead to delayed diagnosis, as noted by the American Gastroenterological Association 1
• Relying solely on TST in BCG-vaccinated individuals can lead to false positives, as recommended by the American Gastroenterological Association 1
• Failing to rule out active TB before starting LTBI treatment can lead to drug resistance and treatment failure, and adding a single drug to a failing regimen can promote further resistance (strong recommendation, moderate quality evidence) 11
• Unnecessary isolation of children with LTBI provides no benefit and may cause psychological harm (strong recommendation, moderate quality evidence) 6
• Anti-TNF agents like adalimumab increase the risk of TB reactivation 4.7-fold compared to placebo in patients with inflammatory bowel disease, and the combination of anti-TNF agents with immunomodulators further increases the risk of TB reactivation 13-fold compared to placebo (according to the European Crohn’s and Colitis Organisation guidelines) 12