What is IgE D farinae?
IgE D farinae is a blood test that measures specific immunoglobulin E antibodies against Dermatophagoides farinae, one of the two major house dust mite species that causes allergic disease. This test identifies sensitization to this particular dust mite allergen and helps diagnose dust mite allergy in patients with perennial allergic symptoms.
Clinical Purpose and Interpretation
The IgE D farinae test detects specific IgE antibodies to Dermatophagoides farinae (Der f), which along with Dermatophagoides pteronyssinus (Der p) accounts for the majority of house dust mite allergies 1. The test should be used in conjunction with clinical history and correlates with symptoms that worsen in dusty environments or are perennial in nature 1.
Key Allergen Components
D. farinae contains two major allergen groups:
- Der f 1 and Der f 2 - these are the primary allergenic proteins
- Approximately 60% or more of mite-sensitive patients react to these major allergen groups 1
- These allergens are immunologically cross-reactive with their D. pteronyssinus counterparts (Der p 1 and Der p 2) 1
Diagnostic Considerations
Test Performance
The predictive value of serum specific IgE testing has important limitations:
- A positive sIgE result (ImmunoCAP class ≥2) was verified by nasal provocation testing in only 69-70% of cases for D. farinae 2
- Even combining positive skin prick test and IgE results yields a positive predictive value of only 0.69 for D. farinae 2
- This means approximately 30% of patients with positive IgE tests may not have clinically relevant allergy
Clinical Application
The selection of allergen immunotherapy should be based on careful history correlated with positive IgE antibodies or skin testing, and should include only clinically relevant allergens 1. For patients being considered for dust mite immunotherapy, nasal provocation testing should be performed to verify clinically relevant allergy before starting therapy 2.
Relationship to Treatment
When specific IgE antibodies to dust mite allergens are confirmed and clinically relevant:
- Immunotherapy for dust mites is effective and should be considered in conjunction with avoidance measures 1
- Due to high cross-allergenicity between D. pteronyssinus and D. farinae, only 50% of the projected amounts of each species needs to be included when preparing immunotherapy extracts 1
- Dust mite immunotherapy has demonstrated significant clinical benefits including decreased bronchodilator use and improved peak expiratory flow rates in patients with mild-to-moderate asthma 1
Important Caveat
Crude house dust extract is an inappropriate substitute for standardized house dust mite extract because it doesn't guarantee inclusion of dust mite proteins and contains non-mite allergens 1. Testing and treatment should use standardized D. farinae extracts specifically.