What labs should be ordered for a patient presenting with nocturnal and morning urticaria (hives) for 2 weeks?

Laboratory Testing for Nocturnal and Morning Urticaria

For a patient with hives occurring only at night and morning for 2 weeks, no routine laboratory testing is required unless specific concerns arise from the patient's history. 1

Initial Approach to Laboratory Testing

According to the 2022 chronic spontaneous urticaria guidelines, laboratory testing should be guided by the patient's history and not performed routinely in all patients with urticaria. The duration of symptoms (2 weeks) classifies this as acute urticaria, which typically requires even fewer investigations.

Key considerations for laboratory workup:

• Duration < 6 weeks: Considered acute urticaria - minimal testing needed
• Pattern of occurrence: Nocturnal/morning pattern may suggest:
  • Physical triggers (e.g., delayed pressure urticaria from bedding)
  • Temperature-related triggers (cold or heat contact urticaria)
  • Possible autoimmune component

Laboratory Testing Algorithm

1. If history is uncomplicated with no systemic symptoms:

   • No laboratory tests are required 1

2. If symptoms persist beyond 6 weeks or history suggests specific concerns:

   • Complete blood count with differential (to detect eosinophilia or leukopenia)
   • Erythrocyte sedimentation rate (ESR)
   • Thyroid function tests and thyroid autoantibodies (especially if autoimmune etiology suspected)

3. If angioedema is present:

   • Serum C4 level (screening test for C1 inhibitor deficiency)
   • If C4 is low, proceed with C1 inhibitor quantitative and functional assays

4. If history suggests food allergy as trigger:

   • Consider specific IgE testing or skin prick testing for suspected allergens 1

Special Considerations

• Timing of symptoms: The nocturnal/morning pattern may suggest:

  • Delayed pressure urticaria (from weight of bedding)
  • Temperature changes during sleep
  • Mast cell degranulation related to circadian rhythm changes

• Diagnostic pitfalls to avoid:

  • Ordering extensive "allergy panels" without specific clinical suspicion
  • Overlooking physical urticaria triggers that may be present in the sleeping environment
  • Missing potential medication causes (especially if taking evening medications)

• When to consider expanded testing:

  • If symptoms are accompanied by systemic manifestations (fever, joint pain)
  • If urticarial lesions last >24 hours (consider urticarial vasculitis)
  • If standard treatments fail to provide relief

Remember that in most cases of acute urticaria, the condition is self-limiting and extensive laboratory evaluation is unnecessary unless the clinical presentation suggests an underlying disorder beyond simple urticaria.