Tuberculosis Screening Guidelines

Introduction

Tuberculosis (TB) screening is crucial for early detection and treatment, particularly in high-risk populations, as recommended by the Centers for Disease Control and Prevention (CDC) and the American Thoracic Society (ATS) 1, 2

The Purified Protein Derivative (PPD) test, also known as the tuberculin skin test (TST), is a standard diagnostic tool for detecting TB infection, with results read 48-72 hours after administration using the Mantoux method 1, 3
Interferon-gamma release assays (IGRAs), such as TB Gold and T-SPOT.TB, are recommended for diagnosing TB infection due to their higher specificity, particularly in BCG-vaccinated individuals and immunocompromised patients 1
IGRAs measure interferon-gamma release in response to specific M. tuberculosis antigens (ESAT-6 and CFP-10) and are not affected by BCG vaccination 1

Individuals at high risk for TB infection, including those with HIV infection, should be screened for TB infection 1, 4, 3
Children with HIV infection have a higher risk of treatment failure and mortality, and TST reactivity is further decreased by HIV infection 5
Annual TST is recommended beginning at age 3-12 months for HIV-infected children 5

Results must be read 48-72 hours after administration, measuring induration (hardened area), not just erythema (redness) 3

The following thresholds for PPD positivity should be used:

Population	Threshold for Positivity
HIV-infected persons, recent contacts of TB cases, persons with fibrotic changes on chest X-ray, and immunosuppressed patients	≥5 mm induration
Recent immigrants from high-prevalence countries, injection drug users, residents of congregate settings, healthcare workers with TB exposure, and persons with certain medical conditions	≥10 mm induration
Persons with no known risk factors	≥15 mm induration

False-negative results can occur in immunocompromised patients, and anergy testing should be considered in HIV-infected patients with companion testing using two DTH skin-test antigens (Candida, mumps, or tetanus toxoid) 3

The diagnosis of pediatric TB is most reliably established through the triad of: a positive tuberculin skin test, abnormal chest radiograph or physical examination, and discovery of a link to a known or suspected case of contagious pulmonary TB, as recommended by the ATS 2
Children with TB often present differently from adults, with rare sputum production, low bacterial load, non-specific symptoms, and differing radiographic findings, according to the CDC 5
Infants with TB may present with progressive respiratory distress, apnea, jaundice, and abdominal distention, and TST may take 2-3 months after infection to become positive, as noted by the ATS 2

Chest radiography should be performed to distinguish between latent TB infection and active TB disease, and follow-up is necessary to read results and provide appropriate care 1, 6
Isoniazid prophylaxis should be considered for PPD-positive patients requiring steroid therapy (≥15 mg prednisone daily for ≥1 month), regardless of the size of PPD reaction, as recommended by the ATS 7
Chest radiography should be included in the evaluation of patients on steroids who are at risk for TB 8

Relying solely on TST results, waiting for bacteriological confirmation before initiating treatment in severely ill children, and failing to investigate potential source cases are common pitfalls in pediatric TB diagnosis, as warned by the ATS 2
Neither PPD nor IGRAs can distinguish between active TB and latent TB infection 1
PPD requires proper administration technique and standardized reading to be reliable, and has a higher false-negative rate (up to 25%) in acutely ill or immunosuppressed patients 9, 10
IGRAs require proper specimen handling to maintain viable white blood cells 1