Assessing Lidocaine Allergy and Skin Testing Dosing
For suspected lidocaine allergy, perform patch testing first with lidocaine 5-10% in petrolatum, followed by intradermal testing with 0.02 mL of preservative-free 1% lidocaine (creating a 3-5 mm bleb) if patch testing is positive, and finally proceed to subcutaneous challenge with 0.1-1.0 mL of 1% lidocaine if intradermal testing is negative.
Assessment Algorithm
Step 1: Clinical History Evaluation
First, determine if the reaction history is consistent with true allergy:
- Test if: Patient reports dermatitis, delayed skin reactions, or suspected hypersensitivity after lidocaine exposure
- Do NOT test if: Patient reports only non-allergic symptoms (headache, vasovagal reactions, anxiety, or family history alone)
True lidocaine allergy is uncommon but increasingly prevalent due to widespread use in over-the-counter products 1.
Step 2: Patch Testing (Initial Screening)
- Concentration: Use lidocaine 5-10% in petrolatum 2
- Interpretation: Positive patch test indicates Type IV delayed hypersensitivity (contact dermatitis)
- Important caveat: Patch testing detects delayed hypersensitivity only, not immediate IgE-mediated reactions
Research shows variable sensitivity with different concentrations: 10% lidocaine yielded 3/4 positive reactions, 5% yielded 4/6 positive, and 1% yielded 3/6 positive 2. Use 5-10% concentration for optimal detection.
Step 3: Intradermal Testing (Confirmation)
If patch test is positive, proceed to intradermal testing:
- Volume: 0.02 mL of preservative-free 1% lidocaine 3, 4
- Technique: Draw up 0.05-0.07 mL, expel excess to obtain exactly 0.02 mL, inject to create a 3-5 mm baseline bleb 3
- Controls: Always place histamine (positive) and saline (negative) controls
- Positive criteria: Wheal ≥3 mm greater than negative control with flare ≥5 mm 3
Critical finding: Studies show that patients with positive patch tests often have negative intradermal tests 5, 4. This discordance is important—negative intradermal testing suggests injectable lidocaine may still be safe.
Step 4: Subcutaneous Challenge (Final Confirmation)
If intradermal testing is negative:
- Dose: 0.1-1.0 mL of preservative-free 1% lidocaine subcutaneously 5, 4
- Observation: Monitor for delayed reactions (up to 48-72 hours)
- Interpretation: Negative challenge indicates injectable lidocaine is safe for future use 5
Key Clinical Pearls
Personnel and Safety Requirements
- Testing must be performed by personnel trained in skin testing interpretation 3
- Have emergency equipment available to treat rare anaphylaxis
- Type IV hypersensitivity (contact dermatitis) does NOT carry anaphylaxis risk 1
Common Pitfalls to Avoid
- Do not use lidocaine with preservatives or epinephrine for testing—use only preservative-free formulations 4
- Do not skip intradermal testing if patch test is positive—patch testing alone overestimates clinical allergy 5
- Do not assume cross-reactivity between amide anesthetics—test alternatives like bupivacaine or mepivacaine separately 2
Alternative Anesthetics
If lidocaine allergy is confirmed:
- Bupivacaine 0.5% showed negative reactions in all 8 tested patients with lidocaine allergy 2
- Consider patch and intradermal testing with alternative amide anesthetics before use
Therapeutic Dosing Context
For reference, therapeutic injectable lidocaine dosing is 50-100 mg IV (not for skin testing) 6, and volumes >30 mL for local anesthesia are generally safe in surgical settings 7. Skin testing uses dramatically lower amounts (0.02-0.1 mL) specifically to detect hypersensitivity without triggering severe reactions.