Tuberculin Skin Test & Mantoux test: Procedure, Nursing Considerations

Tuberculin Skin Test & Mantoux test

Tuberculosis skin test (PPD or Mantoux test) inoculation of tubercle bacillus extract (tuberculin) into the intradermal layer of the inner aspect of the forearm. It is used to detect M. Tuberculosis infection, past or present, active or inactive (latent). 

Equipment 

• Purified protein derivative (PPD) tuberculin antigen intermediate strength. 
• Tuberculin syringe. 
• Short ½" 26 G or 27 G steel needle. 
• Alcohol pad.
• Gloves.

Procedure 

Preparatory phase

• Determine if the patient has ever had bacille calmette Guerin (BCG) vaccine, recent viral disease, immunosuppression by disease, drugs, or steroids.
• Any of these may cause false reading. Previous BCG vaccine or the other factors should not preclude PPD testing, but will be considered with the result. 
• Do not give PPD to person who had had a positive test or TB in the past.
• Chest X-ray is indicated for testing. 

Performance phase 

• Draw up PPD-tuberculin into tuberculin syringe. 
• Follow the manufacturer's directions. Each 0.1 ml dose should contain 5 tuberculin units (TU) of PPD-tuberculin. Use the antigen immediately to avoid absorption onto the plastic/glass syringe. 
• Put on gloves. 
• Follow the standard infection control precautions 
• Clean the skin of the inner aspect of forearm with alcohol. Allow to dry.
• Alcohol must dry for antisepsis. 
• Stretch the skin taut.
• Hold the tuberculin syringe close to the skin so the hub of the needle touches it as the needle is introduced, level up.
• This reduce the needle angle at the skin surface and facilitates the injection of tuberculin just beneath the surface of the skin.
• Inject the tuberculin into the superficial layer of the skin to form a wheat 6 mm to 10  mm in diameter. 
• If no wheal appears (because the injection was made too deep), inject again at another site at least 2 inches (5 cm) away.

Follow up phase

To read the test

• Read the test within 48 to 72 hours when the induration is most evident. 
• Tuberculin skin tests are tests of delayed hypersensitivity. 
• Have a good light available. Flex the patient's forearm slightly at the elbow. 
• Inspect for the presence of induration; inspect from a side view against the light; inspect by direct light.
• Induration refers to hardening or thickening of tissues. 
• Palpate: Lightly rub the finger across the injection site from area of normal skin to the area of induration. Outline the diameter of induration.
• Erythema (redness) without induration is generally considered to be of no significance.
• Measure the maximum transverse diameter of induration (not erythema ) in millimeters with a flexible ruler.
• The extent of induration is measured in two diameters and recorded.

Interpretation 

• Induration of 5 mm or more in diameter indicates positive reaction and need for treatment for latent TB infection in high risk groups.
• High risk group include:
• People with HIV
• People with have had recent contact with active TB.
• People who have fibrotic changes on chest X-ray, consistent with healed TB.
• People with organ transplants or other causes of immunosuppression ( including therapy with ≥ 15 mg /d prednisone ≥ 1 month) or taking TNF -a antagonists.
• Induration of 10 mm or more in diameter indicates a positive reaction and need for treatment of latent TB infection in person at risk.
• Person at risk include.
• people with medical conditions, such as substance abuse, TB within past 2 years, diabetes mellitus, silicosis, head and neck cancer, leukemia, end_stage renal disease, gastrectomy, intestinal bypass, prolonged corticosteroid therapy.
• Recent arrivals ( below 5 years ) from high prevalence countries.
• Injection drug users.
• Mycobacteriology laboratory person
• Health care workers.
• Induration of 15 mm in persons with no known risk factors for TB may be considered for treatment.
• Targeted skin testing program should be conducted among risk-groups only to avoid false positives.