When should a patient with urticaria (hives) be referred for patch testing?

When to Refer Patients with Urticaria for Patch Testing

Patch testing in urticaria is primarily indicated when testing for contact urticarial reactions or when allergic contact dermatitis is suspected as a cause or complicating factor of the patient's skin condition. 1

Primary Indications for Patch Testing in Urticaria

1. When Contact Urticaria is Suspected

• Immediate reactions to substances in direct contact with the skin
• Localized wheals appearing at sites of exposure to specific substances
• History of rapid onset of urticaria following skin contact with potential allergens

2. When Allergic Contact Dermatitis (ACD) Complicates the Clinical Picture

• When urticaria is aggravated by topical medications or emollients 1
• When there are patterns reflecting application of or exposure to consistent items:
  • Marked facial/eyelid involvement
  • Increased severity at neck flexures
  • Vesicular lesions on dorsal hands and fingertips 1
• Unusual or atypical distribution of lesions for typical urticaria 1

Specific Clinical Scenarios Warranting Patch Testing

• Persistent/recalcitrant urticaria not responding to standard therapies 1
• Later onset of disease or new significant worsening without clear trigger 1
• Unusual distribution patterns inconsistent with typical urticaria 1
• Suspected reactions to transdermal patches or topical medications 2
• When urticaria coexists with eczematous lesions, as ACD can be clinically indistinguishable from other skin conditions 1

Testing Considerations

• Antihistamines should be discontinued before patch testing when evaluating for contact urticarial reactions 1
• For standard patch testing (for ACD), antihistamines do not need to be discontinued unless specifically testing for urticaria or contact urticarial reactions 1
• Open patch testing is particularly useful for investigating contact urticaria and protein contact dermatitis 1
• The site should be assessed at regular intervals for the first 30-60 minutes and again after 3-4 days 1

Important Caveats

• Patch testing has a sensitivity and specificity of 70-80% 1, 3
• Positive patch tests only indicate contact sensitization and need demonstrated relevance to the patient's active skin condition 1
• Confirmation may require repeat open application testing of products containing the suspected allergen 1
• Patch testing should be deferred:
  • 6 weeks after natural/artificial UV exposure
  • 3 months after finishing systemic agents
  • 6 months after finishing biological agents 1

Testing Process

1. Apply suspected allergens to unaffected skin (typically the back)
2. Leave in place for 48 hours
3. Assess reactions at time of patch removal
4. Perform additional readings up to 7 days after application to detect delayed reactions 1
5. For contact urticaria, use open patch testing with assessment within the first 30-60 minutes 1

By following these guidelines, clinicians can appropriately identify patients with urticaria who would benefit from patch testing, potentially identifying triggers that can be avoided to improve disease control and quality of life.