TB Skin Test Dosing
Draw up exactly 0.1 mL of tuberculin containing 5 tuberculin units (TU) of purified protein derivative (PPD). This is the standardized dose for intradermal (Mantoux) tuberculin skin testing 1, 2.
Preparation Details
The CDC guidelines and FDA labeling are unequivocal on this point:
- Volume: Exactly 0.1 mL
- Concentration: 5 TU PPD per 0.1 mL dose
- Syringe: Use a 1 mL syringe calibrated in tenths
- Needle: 26 or 27 gauge, one-quarter to one-half inch length 1, 2
Drawing Up Technique
When preparing the dose 1:
- Remove the PPD vial from refrigeration immediately before drawing
- Clean the vial stopper with antiseptic and allow to dry
- Draw slightly more than 0.1 mL into the syringe
- Remove excess volume or air bubbles to exactly 0.1 mL while the needle remains in the vial to avoid wasting antigen
- Return the vial to refrigeration immediately after filling
Critical Administration Points
The injection must be intradermal only - not subcutaneous, intramuscular, or intravenous 2. When properly administered, a definite pale wheal (bleb) approximately 10 mm in diameter should form at the injection site 1. If no wheal forms, the test was improperly administered and must be repeated immediately at another site at least 2 inches away 1.
Common Pitfalls to Avoid
- Do not use multiple puncture tests (Tine, Heaf) or non-standard PPD strengths (1 TU or 250 TU) - these are insufficiently accurate 3
- Do not draw up more or less than 0.1 mL - the standardized dose is critical for accurate interpretation
- Do not allow the vial to warm - fill immediately after removing from refrigeration 1
- If subcutaneous injection occurs, the test cannot be interpreted and must be repeated 2
The 5 TU/0.1 mL dose has been standardized through extensive US Public Health Service studies to ensure bio-equivalency with the US Standard Tuberculin PPD-S 2. This standardization eliminates batch-to-batch variation and ensures reliable, interpretable results across different testing sites and populations.