What laboratory tests should be checked for a patient presenting with dermatographism?

Laboratory Testing for Dermatographism

For patients with dermatographism, no specific laboratory tests are routinely indicated as the diagnosis is primarily clinical, confirmed through a provocation test or dermatographic test. 1

Diagnostic Approach

Primary Diagnostic Method

• Clinical diagnosis: Dermatographism is diagnosed through:
  • Medical history of linear wheals after scratching or friction
  • Provocation test (stroking the skin with a tongue blade to elicit linear wheals with flare and itching) 1, 2

Laboratory Testing Considerations

When Laboratory Tests May Be Considered:

1. When symptoms are atypical or refractory to treatment
2. When other conditions are suspected

Potential Laboratory Tests to Consider:

• Skin testing alternatives:

  • In vitro specific IgE (sIgE) tests may be useful when skin testing is contraindicated due to dermatographism 3
  • Specific IgE immunoassays have approximately 70-75% sensitivity compared to skin prick tests 3

• Evaluation for associated conditions:

  • Thyroid function tests: Consider if thyroid disease is suspected 2
  • Complete blood count: To evaluate for eosinophilia if atopy is suspected 4
  • Total serum IgE: May be elevated in atopic individuals, but has poor diagnostic value alone 3, 5

Important Considerations

Limitations of Testing

• Total serum IgE levels alone have insufficient sensitivity and specificity for diagnosing allergic conditions 3
• The ratio of specific IgE to total IgE offers no advantage over specific IgE alone in diagnosing food allergies 3

Special Situations

• Skin testing challenges: Patients with dermatographism may have false-positive skin test results due to their skin's hyperreactivity 3, 6
• Alternative testing: In vitro specific IgE testing is preferable when:
  • Widespread skin disease is present
  • Patient has severe dermatographism
  • Patient is on medications that suppress skin test reactions
  • Patient is uncooperative 3

Management Implications

• Laboratory testing should not be used to monitor treatment efficacy 5
• Testing should be performed when:
  • Patients don't respond to empiric treatment
  • Identification of specific allergens could affect therapy decisions 5

Common Pitfalls to Avoid

• Overreliance on laboratory testing without clinical correlation 5
• Unnecessary extensive testing that doesn't impact management 5
• Failure to consider comorbidities that may be associated with dermatographism 2

Remember that dermatographism may be associated with certain conditions including psychic factors (30%), atopy (12.5%), drug reactions (7.5%), hyperthyroidism (5%), and rarely with diabetes, menopause, or infectious diseases 2. However, these associations don't necessarily require routine laboratory screening unless clinically indicated.