Conjoint Allergy & Immunology: Atopy, Anaphylaxis, and Immunodeficiency Clues
Core concepts
Allergy questions test the atopic march (eczema, then IgE-mediated food allergy, allergic rhinitis, asthma), the difference between IgE-mediated (immediate, mast-cell driven) and non-IgE-mediated (delayed, cell-mediated, e.g., food protein–induced enterocolitis) reactions, and the diagnostic value of history over testing. Skin prick and specific IgE tests detect sensitization; a positive test without compatible history is not allergy. Component testing and oral food challenge clarify ambiguous cases.
Know anaphylaxis criteria: acute onset with skin/mucosal involvement plus respiratory compromise or hypotension, or two or more organ systems after a likely allergen, or hypotension after exposure. Epinephrine intramuscularly into the anterolateral thigh is first-line; antihistamines and steroids are adjuncts, never substitutes. Prescribe an autoinjector and an action plan.
For immunodeficiency, recognize warning signs: recurrent severe or unusual infections, failure to thrive, chronic diarrhea, family history, and live-vaccine complications. Distinguish antibody defects (sinopulmonary infections) from T-cell/combined defects (opportunists, severe viral illness) and phagocyte defects (skin abscesses, catalase-positive organisms).
Traps
- Withholding epinephrine while waiting for antihistamines to work.
- Diagnosing food allergy from a positive panel alone.
- Missing that eczema with failure to thrive, diarrhea, and petechiae suggests immune dysregulation rather than simple atopy.
Rule of thumb
"History plus exposure equals diagnosis; test only what the history implicates." For anaphylaxis, dose epinephrine 0.01 mg/kg of 1 mg/mL IM (max 0.5 mg) and repeat every 5–15 minutes as needed.