how to give a tb test

3 min read 30-12-2024

Meta Description: Learn the step-by-step procedure for administering a tuberculin skin test (TST), including patient preparation, injection technique, and post-test instructions. This guide is for healthcare professionals only.

This article provides a detailed guide for healthcare professionals on how to administer a tuberculin skin test (TST), also known as a Mantoux test. This is not intended for self-administration or lay audiences. Improper administration can lead to inaccurate results and should only be performed by trained medical professionals.

Understanding the Tuberculin Skin Test (TST)

The TST is an important tool for screening individuals for latent tuberculosis infection (LTBI). It involves injecting a small amount of tuberculin purified protein derivative (PPD) under the skin. A positive reaction indicates exposure to Mycobacterium tuberculosis, but doesn't necessarily mean active TB disease. Further testing is needed to confirm active TB.

Types of TB Tests

While the TST is a common method, other tests exist, including the interferon-gamma release assays (IGRAs). IGRAs, like QuantiFERON-TB Gold and T-SPOT.TB, directly measure the immune response to TB bacteria. These tests can differentiate between LTBI and previous BCG vaccination more reliably than the TST. However, the TST remains widely used due to its cost-effectiveness and established protocols.

Step-by-Step Guide to Administering a TST

Before you begin: Ensure you have all necessary supplies: tuberculin syringe (1 ml, 27-gauge needle), tuberculin PPD solution, alcohol swabs, gloves, gauze pads, sharps container, and patient information.

1. Patient Preparation and Identification

Verify patient identity: Confirm the patient's identity using two identifiers (e.g., name and date of birth).
Explain the procedure: Clearly explain the procedure to the patient, including potential side effects (e.g., slight redness, swelling, itching at the injection site).
Hand hygiene: Perform thorough hand hygiene before initiating the procedure.
Gloves: Don clean gloves.

2. Preparing the Injection Site

Site Selection: Choose the volar surface of the forearm, approximately 3-4 inches below the antecubital fossa. Avoid areas with scars or lesions.
Clean the site: Cleanse the injection site with an alcohol swab using a circular motion, moving outward from the center. Allow the site to air dry completely.

3. Injecting the PPD

Syringe Preparation: Draw up the prescribed amount of PPD (usually 0.1 ml) into the tuberculin syringe. Ensure there are no air bubbles.
Injection Technique: Insert the needle bevel up at a 10-15 degree angle into the intradermal layer of the skin. Slowly inject the PPD, creating a small wheal (a raised, pale area) approximately 6-10 mm in diameter. Avoid subcutaneous injection.
Needle Removal: Withdraw the needle smoothly. Do not massage the injection site.

4. Post-Injection Instructions

Documentation: Document the date, time, batch number of the PPD, site of injection, and the size of the wheal in the patient's medical record.
Patient Instructions: Instruct the patient to return for reading of the test 48-72 hours later. Advise them not to cover the injection site or wash it vigorously.

5. Reading the Test

Measurement: The TST is read by measuring the induration (hardened area), not erythema (redness). Use a clear ruler to measure the transverse diameter of the induration in millimeters.
Interpretation: Interpretation of the test result depends on the patient's risk factors and the size of the induration. Consult your local guidelines and references for specific interpretation criteria.

Potential Complications and Precautions

Though rare, complications can include allergic reactions or local infection at the injection site. Follow proper aseptic technique and be aware of potential allergies to prevent complications.

Conclusion

Administering a TST accurately is crucial for detecting latent TB infection. Following these steps and adhering to established guidelines helps ensure accurate results and contributes to effective tuberculosis control. Remember, proper training and adherence to established protocols are paramount when performing this procedure. Consult your local health authority for the most current guidelines and interpretations. This information should not be considered a substitute for formal medical training.