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Introduction ⬇

These tests diagnose TB-infected persons who are at increased risk for TB development and who will benefit from treatment. The QuantiFERON-TB Gold Plus test (QFT-Plus) is a test used to detect active or latent TB infection (LTBI), but should not be used alone to diagnose TB. The QFT-Plus measures interferon gamma, a component of cell-mediated immune activity to TB response, as well as stimulates CD4 and CD8 antigens, which provides a better picture of immune response. Tuberculin skin testing (TST) screens for new or LTBI in high-risk groups. The TST measures lymphocyte response to TB in persons sensitized to the TB antigen. This test has been used for years and measures a delayed hypersensitivity response (48–72 hours). QFT-Plus produces fewer false-positive results than the TST and, according to the Centers for Disease Control and Prevention (CDC), can be used interchangeably with the TST in all situations to diagnose M. tuberculosis infection.

  1. A positive QFT-Plus result (≥0.35 IU/mL) indicates that TB infection is likely.

  2. A negative QFT-Plus result indicates that TB infection is unlikely but cannot be excluded.

Procedure ⬆ ⬇

  1. Obtain a 1-mL venous blood sample × 4 tubes in QFT-Plus kit.

  2. Shake tubes firmly (10 times) to ensure inner surface of the tubes is coated with blood.

  3. See description in Tuberculin Skin Test (TB Test); Two-Step TB Test section.

Interventions ⬆ ⬇

Pretest Patient Care

  1. Explain purpose of test, procedure for specimen collection, and interfering factors.

  2. Follow guidelines in Chapter 1 for safe, effective, informed pretest care.

Posttest Patient Care

  1. Review test results; report and record findings. Modify the nursing care plan as needed. Counsel the patient appropriately.

  2. Follow guidelines in Chapter 1 for safe, effective, informed posttest care.

Interfering Factors ⬆ ⬇

  1. Diabetes, silicosis, and chronic kidney disease may decrease responsiveness to both the TST and QFT-Plus tests.

  2. Treatment with immunosuppressive drugs has been shown to decrease the response to the TST.

  3. Some of the hematologic disorders, such as leukemia and lymphoma, may decrease response to the TST and QFT-Plus test.

Reference Values ⬆

Normal

QFT-Plus: negative

TST: negative for cutaneous hypersensitivity—area of induration, lesser than 10 mm (unless person is HIV positive, had recent contact with person with TB, had an organ transplant, or is immunosuppressed, in which case lesser than 5 mm)