Two types of tests are used to detect the immune response to M. tuberculosis and are used to screen patients for latent tuberculosis and investigation of active tuberculosis. The TST response to tuberculin antigen is a manifestation of a T cell−mediated delayed hypersensitivity. The Mantoux test, an intradermal injection of 5 TU (tuberculin units) of purified protein derivative standard (PPD-S), usually on the volar surface of the forearm, is the standard TST. It is usually positive 2 to 6 weeks after onset of infection (occasionally 3 months) and at the time of symptomatic illness. This test is preferred in children less than 5 years of age. It may also be used in other settings such as contact investigations or in older patients. Only persons at high risk should be offered a Mantoux test (Table 124-1). False-negative responses may occur early in the illness, with use of inactivated antigen (as a result of poor storage practice or inadequate administration), or as a result of immunosuppression (secondary to underlying illness, AIDS, malnutrition, or overwhelming tuberculosis). Tests with questionable results should be repeated after several weeks of therapy and adequate nutrition. Because of poor nutrition, a high proportion of internationally adopted children arriving in the United States have an initial false-positive TST. All internationally adopted children with an initially negative TST should have a repeat TST after 3 months in the United States. The TST is interpreted based on the host status and size of induration (Table 124-2).
Table 124-1 Tuberculin Skin Test (TST) Recommendations for Infants, Children, and Adolescents* CHILDREN FOR WHOM IMMEDIATE TST OR IGRA IS INDICATED:†
Contacts of people with confirmed or suspected contagious tuberculosis (contact investigation)
Children with radiographic or clinical findings suggesting tuberculosis disease
Children immigrating from countries with endemic infection (e.g., Asia, Middle East, Africa, Latin America, countries of the former Soviet Union), including international adoptees
Children with travel histories to countries with endemic infection and substantial contact with indigenous people from such countries
Children infected with HIV infection (TST only)
Children with other medical conditions, including diabetes mellitus, chronic renal failure, malnutrition, and congenital or acquired immunodeficiencies deserve special consideration. Without recent exposure, these people are not at increased risk of acquiring tuberculosis infection. Underlying immune deficiencies associated with these conditions theoretically would enhance the possibility for progression to severe disease. Initial histories of potential exposure to tuberculosis should be included for all of these patients. If these histories or local epidemiologic factors suggest a possibility of exposure, immediate and periodic TST or IGRA should be considered. An initial TST or IGRA should be performed before initiation of immunosuppressive therapy, including prolonged steroid administration, use of tumor necrosis factor-alpha antagonists, or other immunosuppressive therapy in any child requiring these treatments.
Recommendations from American Academy of Pediatrics: Tuberculosis. In
Pickering LK, Baker CJ, Kimberlin DW, et al, editors. Red Book: 2012 Report of the Committee on Infectious Diseases, ed 29, Elk Grove Village, IL, 2012,
American Academy of Pediatrics. HIV, Human immunodeficiency virus; IGRA, interferon-gamma release assay;
LTBI, latent tuberculosis infection. *Bacille Calmette-Guérin immunization is not a contraindication to a TST.
†Beginning as early as 3 months of age.
‡If the child is well, the TST or IGRA should be delayed for up to 10 weeks after return.