To perform a PPD (Purified Protein Derivative) skin test, also known as a Mantoux tuberculin skin test, the process primarily involves precise patient positioning, site selection, and the correct intradermal injection technique.
The PPD skin test is a common method used to screen for tuberculosis (TB) infection. It involves injecting a small amount of tuberculin protein derivative into the skin, and then observing the reaction after 48 to 72 hours. The correct administration is crucial for accurate results.
Preparing for PPD Administration
Before administering the PPD skin test, ensure you have all necessary supplies and the patient is ready.
Essential Supplies:
- PPD solution (tuberculin PPD)
- Tuberculin syringe with a 27-gauge, 1/2-inch needle
- Alcohol swab
- Gloves
- Marking pen (optional, to mark the site)
- Patient instructions for follow-up reading
Step-by-Step PPD Skin Test Administration
The administration of a PPD test requires a careful, sterile technique to ensure the medication is delivered correctly into the intradermal layer of the skin.
1. Patient Positioning & Site Selection
Proper patient positioning and site selection are vital for a successful intradermal injection:
- Positioning: Have the patient sit comfortably. According to expert guidance, on a firm surface, have the patient extend their left arm palms side up and slightly flexed at the elbow. This provides a stable and accessible injection site.
- Site Selection: The preferred site is the volar (inner) surface of the forearm. Measure approximately two to four inches below the elbow on the forearm for the injection site. This area is typically hairless, free of lesions, and has less pigmentation, making the reaction easier to read. Avoid areas with visible veins, scars, or dermatitis.
2. Preparing the Injection Site
- Cleanse: Cleanse the selected injection site thoroughly with an alcohol swab. Use a circular motion, moving outwards from the center. Allow the alcohol to air dry completely; do not fan or blow on the site.
- Don Gloves: Put on clean gloves to maintain aseptic technique.
3. Administering the Intradermal Injection
The PPD test is administered via an intradermal injection, meaning the solution is injected into the dermal layer of the skin, just below the epidermis.
- Prepare Syringe: Draw up 0.1 mL of PPD solution into the tuberculin syringe, ensuring no air bubbles are present.
- Stretch Skin: Grasp the patient's forearm firmly from underneath and stretch the skin taut at the injection site.
- Insert Needle: Hold the syringe with the bevel of the needle facing upwards. Insert the needle slowly into the skin at a very shallow angle (5 to 15 degrees) until the entire bevel is just under the skin surface. You should be able to see the outline of the needle through the epidermis.
- Inject Solution: Slowly inject the PPD solution. A proper injection will produce a distinct, pale elevation of the skin, often called a "wheal" or "bleb," approximately 6-10 mm in diameter. If no wheal appears, or if leakage occurs, the test may need to be repeated at a different site or on the other arm.
- Withdraw Needle: Once the solution is injected and the wheal has formed, gently and quickly withdraw the needle at the same shallow angle.
- Do Not Massage: Do not massage or rub the injection site, as this can cause the solution to disperse into subcutaneous tissue, leading to an inaccurate result.
4. Post-Injection Care & Instructions
- Education: Instruct the patient not to scratch, rub, or cover the injection site with bandages or tape. They can wash the area gently.
- Follow-Up: Provide clear instructions on when and where to return for the test reading (typically 48 to 72 hours after injection). Emphasize the importance of timely reading for accurate interpretation.
Reading the PPD Test
The PPD test is read by measuring the diameter of the induration (a firm, raised area, not just redness) at the injection site. This measurement is crucial for determining a positive or negative result, which is interpreted based on specific clinical guidelines and the patient's risk factors.
