What allergy testing is recommended for a patient with urticaria after using Dreft (laundry detergent)?

Allergy Testing for Urticaria After Laundry Detergent Exposure

Patch testing is the recommended allergy testing for a patient who developed hives after using Dreft laundry detergent, as it is the gold standard for diagnosing contact allergens that may cause urticaria. 1

Diagnostic Approach for Detergent-Related Urticaria

Initial Assessment

• Determine if the reaction was immediate (within minutes to hours) or delayed (24-48 hours)
• Document the distribution pattern of hives (localized to clothing contact areas or generalized)
• Ask about previous reactions to other detergents or similar products

Recommended Testing

1. Patch Testing

   • Gold standard for diagnosing allergic contact dermatitis and contact urticaria 1
   • Apply suspected allergens to the back under occlusion for 48 hours
   • Read results at 48 hours, with additional readings at 72-96 hours
   • Include:
     • Standard allergen series (captures ~80% of common allergens) 1
     • Detergent series (including optical brighteners, enzymes, fragrances)
     • The actual Dreft detergent diluted to 0.1% aqueous solution 2

2. Open Patch Testing

   • Useful for assessing potential irritants or contact urticaria 1
   • Apply diluted detergent (0.1% solution) to forearm
   • Assess for immediate reactions within 30-60 minutes and delayed reactions after 3-4 days

3. Repeated Open Application Test (ROAT)

   • Apply diluted detergent twice daily for up to a week on forearm
   • Stop if reaction develops
   • Helps differentiate between irritant and allergic reactions 1

Special Considerations

When to Consider Additional Testing

• If standard patch testing is negative but clinical suspicion remains high:
  • Consider testing with additional detergent components
  • Test for fragrance allergens (common in detergents) 2
  • Consider systemic contact dermatitis evaluation if symptoms are widespread 1

Limitations and Precautions

• Patch testing should be deferred for:
  • 6 weeks after UV exposure
  • 3 months after systemic immunosuppressants
  • 6 months after biological agents 1
• False negatives may occur if patient is on antihistamines or corticosteroids
• False positives may occur due to irritant reactions from detergents 2

Interpreting Results

• Positive patch test with clinical correlation confirms allergic contact dermatitis
• Immediate positive reaction to open patch test suggests IgE-mediated contact urticaria 1
• Negative results with convincing history may still warrant avoidance of the product

Management After Testing

• Complete avoidance of identified allergens
• Consider fragrance-free, dye-free detergents
• Double rinsing of laundry may help reduce residual detergent exposure
• Patient education about cross-reactive substances and hidden sources

Common Pitfalls

• Detergent allergy is relatively rare (0.7% in one study) and many reactions may be irritant rather than allergic 2
• Distinguishing between irritant and allergic reactions can be challenging
• Not testing with the actual product used by the patient
• Failing to consider other components in detergents beyond the main surfactants
• Overlooking systemic manifestations of contact allergens

Patch testing remains the most reliable diagnostic tool for evaluating detergent-related urticaria, though the prevalence of true allergic reactions to modern detergents is relatively low 2, 3.