What is the proper procedure for administering a Mantoux test (Tuberculin Skin Test)?

How to Properly Administer the Mantoux Tuberculin Skin Test

The Mantoux tuberculin skin test must be administered by injecting 0.1 ml of 5-TU PPD intradermally into the volar or dorsal surface of the forearm, creating a 6-10 mm wheal, and read 48-72 hours later by measuring induration (not redness) in millimeters. 1

Proper Administration Technique

Preparation:

• Select the volar (inner) or dorsal (outer) aspect of the forearm as the preferred site
• Avoid areas with lesions, visible veins, or inflammation 1, 2
• Clean the site with a suitable germicide and allow to dry 2
• Use a 1 mL syringe calibrated in tenths and fitted with a 26-27 gauge needle, ¼ to ½ inch in length 1, 2

Injection Technique:

1. Draw exactly 0.1 mL of 5-TU PPD tuberculin into the syringe 1, 2
2. Insert the needle bevel-up into the most superficial layers of the skin (intradermal) 1, 2
3. Inject slowly to form a pale, discrete wheal (bleb) 6-10 mm in diameter 1
4. Do not dress or cover the site 2
5. If a wheal does not form, the test was improperly administered and should be repeated at least 2 inches away from the original site 1, 2

Reading the Test

Timing:

• Read the test between 48-72 hours after administration 1
• Tests read after 72 hours may underestimate the true size of induration 1
• Research suggests readings at 72 hours may be more accurate than at 48 hours, as reactions tend to be larger at 72 hours 3

Reading Technique:

1. Read in good lighting with the forearm slightly flexed at the elbow 1
2. Look for induration (raised, hardened area), not redness 1, 2
3. Measure the diameter of induration transversely to the long axis of the forearm 1, 2
4. Record the measurement in millimeters (including "0 mm" if no induration) 1, 2
5. The ball-point pen method of Sokal can help decrease interobserver variability:
   • Gently push a ballpoint pen at a 45° angle toward the injection site
   • The pen will stop at the edge of induration 1, 2

Important Considerations

Documentation:

• Record the technique used (Mantoux)
• Record the dose and type of tuberculin used (5-TU PPD)
• Record the size of reaction in millimeters of induration 1
• If a second test was administered due to improper technique, note the site used 1

Common Pitfalls to Avoid:

• Using multiple puncture tests instead of the Mantoux method (less reliable) 1
• Subcutaneous rather than intradermal injection (invalidates results) 2
• Measuring erythema (redness) instead of induration 1, 2
• Recording results as "positive" or "negative" rather than actual measurements in millimeters 1
• Self-reading by patients (strongly discouraged) 2
• Improper storage of tuberculin (should be refrigerated, not frozen, and protected from light) 1

Special Considerations:

• False-negative results may occur in up to 25% of people with active tuberculosis, particularly in those who are immunosuppressed 1
• BCG vaccination history does not preclude tuberculin skin testing 1, 4
• Live-attenuated virus vaccines may cause false-negative PPD results if administered before the tuberculin test 1

By following these standardized procedures for administration and reading of the Mantoux tuberculin skin test, healthcare providers can ensure accurate results for proper diagnosis and management of tuberculosis infection.