Two-Step Tuberculin Skin Testing Protocol

Purpose and Eligibility

The two-step TST protocol is used to detect the "booster phenomenon" in individuals with waned TB immunity, preventing misinterpretation of boosted reactions as new infections during subsequent serial testing, as recommended by the Centers for Disease Control and Prevention (CDC) 1
Two-step testing should be performed on all newly employed healthcare workers who have an initial negative TST and no documented negative TST within the preceding 12 months, according to the CDC guidelines 1
The American Thoracic Society recommends two-step testing for healthcare workers in facilities conducting periodic TB screening, staff in correctional institutions and nursing homes, populations with high rates of prior TB exposure or BCG vaccination, and older adults 2

The first TST should be placed on Day 0 using the Mantoux technique, and read at 48-72 hours (Day 2-3) by measuring only the induration, as recommended by the CDC 1
The second TST should be placed 1-3 weeks after reading the first test (approximately Day 9-24), and read again at 48-72 hours, according to the CDC guidelines 1

Both tests negative: True negative baseline established; individual can proceed with annual or periodic screening as indicated by risk classification, as recommended by the CDC 2
First test negative, second test positive: This represents a boosted reaction from prior TB exposure or BCG vaccination, not a new infection, according to the CDC guidelines 1

For individuals unlikely to return for multiple visits, interferon-gamma release assays (IGRAs) may be considered as they require only a single blood draw without return visits for reading, as suggested by the European Centre for Disease Prevention and Control (ECDC) 4, 5, 6