American Board of Allergy and Immunology Exam Study Guide

Preparing for the American Board of Allergy and Immunology is a professional milestone — you want study material that respects your time and reliably improves performance. If you’re deciding which resources to buy, look for content that blends realistic practice questions, concise high-yield summaries, and explanations that translate immunology into clinical decisions. Whether you need a full-length practice simulation or targeted topic review, choose materials that help you focus quickly on weaknesses and build confident test-day habits.

What is the ABAI exam?

The ABAI exam certifies physicians in Allergy and Immunology by testing clinical reasoning, problem-solving, and foundational science relevant to everyday practice. The exam asks you to interpret diagnostic data, weigh management options, and apply immunologic principles across common and complex scenarios — from anaphylaxis and asthma phenotyping to evaluation of primary immunodeficiency. Good preparation integrates core knowledge with repeated exposure to exam-style items so you become fluent at translating lab results and histories into safe, evidence-based plans.

How a smart study product helps: what to expect

A high-quality ABAI Exam Prep package should include realistic question banks, concise topic summaries, and analytics so you track progress. Use an ABAI Practice Test early to set a baseline and again under timed conditions before exam day. Quality explanations matter: they should explain why an answer is correct, how to interpret borderline labs (e.g., paired tryptase timing), and when real-world management deviates from textbook answers.

Core topics (mapped to practical study areas)

Below are the themes you’ll encounter frequently — each item reflects the kinds of concepts emphasized in exam-style Allergy and Immunology Practice Questions:

• Anaphylaxis and acute management
  Recognition, immediate treatment (intramuscular epinephrine), positioning, and special circumstances (pregnancy, tryptase interpretation, biphasic reactions). Practice questions emphasize timing and triage.
• Asthma: phenotypes and therapeutics
  Distinguish type-2 high vs non-type-2 disease using FeNO, blood eosinophils, and clinical features. Know biologic indications (anti-IL-5, anti-IL-4Rα, anti-IgE), inhaled steroid strategies, and when bronchial thermoplasty or add-on therapies are considered.
• Drug and vaccine hypersensitivity
  Immediate vs delayed reactions, penicillin skin testing and oral challenge strategies, DRESS and SJS/TEN recognition, and desensitization protocols for essential therapies.
• Primary and secondary immunodeficiencies
  Newborn SCID screening (TRECs), CVID patterns and GLILD, X-linked agammaglobulinemia (BTK), CGD pathophysiology and prophylaxis, DOCK8/STAT3 presentations, selective IgA/IgM defects, and secondary causes like protein-losing enteropathies.
• Mast cell, bradykinin, and angioedema disorders
  Systemic mastocytosis (baseline tryptase interpretation), hereditary angioedema (C1-INH antigenic vs functional testing), ACE inhibitor angioedema mechanisms, and targeted therapies (C1-INH concentrate, icatibant, kallikrein inhibitors).
• Eosinophilic diseases & vasculitis
  Hypereosinophilic syndromes, EGPA phenotypes (ANCA-positive vs negative), eosinophilic esophagitis, and how anti-IL-5/IL-5R agents are applied.
• Allergic diagnostics and component testing
  Role of skin prick testing, specific IgE, component-resolved diagnostics (e.g., Ara h2), BAT and when to use each test to refine risk and counseling.
• Occupational & contact disease
  Occupational asthma evaluation (serial PEFR, specific inhalation challenge), patch testing for contact dermatitis, and hypersensitivity pneumonitis identification.
• Special and emerging topics
  Autoinflammatory syndromes, IgG4-related disease, pharmacogenetics (TPMT/NUDT15 for azathioprine), immunizations for immunocompromised hosts, and microbiome implications in allergy risk.

Who can take the exam — and who benefits from prep resources?

• Eligible candidates: Physicians completing accredited allergy/immunology training or otherwise board-eligible per ABO requirements.
• Who benefits most from ABAI practice materials: Fellowship candidates, clinicians preparing for recertification, and educators building question banks. Short, targeted ABAI Practice Exam sessions help fellows identify weak domains and structure revision during busy clinical rotations.
• Useful for: Specialists who manage complex asthma, immunodeficiency clinics, drug allergy evaluations, and those prescribing biologics.

How to use practice questions effectively

• Begin with a timed ABAI Practice Test to benchmark performance.
• Target weak domains (identified by analytics) with focused study blocks: e.g., 48–72 hours on immunodeficiency, then move to drug allergy.
• Mix learning modes — read a concise ABAI Study Guide for Knowledge topics, then reinforce with case questions and flashcards.
• Review every explanation. For each missed question, summarize the key teaching point in one sentence — this converts mistakes into durable learning.

High-impact study tips (practical and time-efficient)

1. Prioritize safety-critical scenarios first: anaphylaxis, SJS/TEN, HAE, and acute immunodeficiency workup.
2. Use spaced repetition for immunology pathways and drug-gene associations.
3. Simulate test day by taking full practice exams under timed conditions to build stamina.
4. Translate practice mistakes into protocols — e.g., create a one-page anaphylaxis algorithm, a flowchart for suspected HAE, and a checklist for immunodeficiency screening.
5. Discuss difficult cases with peers or mentors; teaching a concept is one of the fastest ways to learn it.
6. Practice interpreting paired labs (tryptase, C1-INH antigen vs function, vaccine serologies) rather than memorizing single cutoff values.

The right ABAI Exam Prep supports more than recall: it helps you think clinically under pressure. Invest in a balanced package — realistic ABAI Practice Exams, an evidence-based ABAI Study Guide for Knowledge, and a set of curated Allergy and Immunology Practice Questions that mirror the cognitive level of the real test. With focused practice, active review, and systems-level checklists for emergencies, you’ll enter exam day with both knowledge and the confidence to apply it.

ABAI Sample Questions and Answers

A 28-year-old woman has seasonal allergic rhinitis every spring. Skin prick testing demonstrates a 7 mm wheal to a standardized tree pollen extract and negative saline control. Her total serum IgE is normal. Which statement about the skin test result is MOST accurate?

A. A 7 mm wheal is a false positive unless the histamine control is >10 mm.
B. Skin prick wheal diameter must be interpreted relative to negative and positive controls and not solely to total IgE.
C. Normal total IgE rules out clinically relevant IgE-mediated allergy.
D. A positive skin test to an inhalant allergen always means immunotherapy will be effective.

Answer: B.

Explanation: Skin prick testing interpretation depends on comparison with the negative (saline) and positive (histamine) controls, and results are reported as wheal diameter relative to those controls. A 7 mm wheal with an appropriate histamine control indicates sensitization. Total serum IgE can be normal in patients with clinically relevant specific IgE; it does not exclude IgE-mediated allergy. Not all sensitizations are clinically relevant, and immunotherapy effectiveness requires correlation of history, exposure, and testing. Clinical correlation and control responses are essential when interpreting skin tests.

Which cytokine is most centrally associated with class switching to IgE production by B cells?

A. IFN-γ
B. IL-4
C. IL-17
D. TGF-β

Answer: B. IL-4

Explanation: IL-4 is the primary cytokine driving B-cell class switching to IgE in the setting of Th2-type immune responses; it induces expression of germline ε transcripts and activates transcription factors necessary for IgE isotype switching. IL-13 shares overlapping effects with IL-4 in promoting allergic inflammation and airway hyperresponsiveness. IFN-γ tends to promote IgG2a and inhibit IgE class switching; IL-17 and TGF-β have different roles in neutrophilic inflammation and regulatory or IgA pathways, respectively. Understanding the central role of IL-4 helps explain allergic pathogenesis and therapeutic targets (e.g., anti-IL-4/IL-13 agents).

A patient with chronic spontaneous urticaria (CSU) has persistent daily wheals despite high-dose second-generation H1 antihistamine (up to 4× standard dose). According to current guideline-based steps, the next appropriate therapy is:

A. Switch to first-generation H1 antihistamine.
B. Add a leukotriene receptor antagonist as first escalation.
C. Add omalizumab.
D. Start high-dose systemic corticosteroids.

Answer: C. Add omalizumab.

Explanation: Contemporary management of antihistamine-refractory CSU recommends escalation to omalizumab (anti-IgE monoclonal antibody) before chronic systemic corticosteroids. Leukotriene receptor antagonists may have adjunctive benefit in some patients but are not the primary next step for antihistamine-refractory disease. Long-term or repeated high-dose systemic corticosteroids are discouraged due to adverse effects; short courses may be used for severe flares. Omalizumab has RCT-level evidence of efficacy and good tolerability in CSU nonresponsive to high-dose H1 blockers.

Which laboratory test is most useful to confirm mast cell activation in a patient evaluated for possible anaphylaxis hours after symptom onset?

A. Total serum IgE
B. Serum tryptase (sampled 1–4 hours after onset)
C. Skin biopsy for mast cells
D. Peripheral eosinophil count

Answer: B. Serum tryptase (sampled 1–4 hours after onset)

Explanation: Serum tryptase is released from mast cells during anaphylactic reactions and peaks typically within 1–2 hours and remains elevated for several hours; sampling within 1–4 hours of symptom onset is recommended to detect mast cell activation. A baseline (≥24 hours later) sample can be compared to the acute level; an acute rise (e.g., >20% + 2 ng/mL above baseline) supports mast cell activation. Total IgE does not confirm an acute reaction; skin biopsy is not helpful acutely; peripheral eosinophils are not specific for anaphylaxis. Timely collection is essential for interpretation.

Which of the following best describes the mechanism of action of omalizumab?

A. Binds free IL-5 to reduce eosinophil production.
B. Binds circulating IgE at the Fc region, preventing IgE from binding to FcεRI.
C. Binds the IL-4 receptor α chain blocking IL-4/IL-13 signaling.
D. Antagonizes leukotriene D4 receptor.

Answer: B. Binds circulating IgE at the Fc region, preventing IgE from binding to FcεRI.

Explanation: Omalizumab is a monoclonal antibody that binds the Fc portion of circulating IgE (Cε3 region), lowering free IgE levels and preventing IgE binding to high-affinity FcεRI receptors on mast cells and basophils. This leads to downregulation of FcεRI expression over time and reduces allergic effector cell activation. Anti-IL-5 agents (e.g., mepolizumab) target IL-5; dupilumab blocks IL-4Rα to inhibit IL-4/IL-13 signaling. Leukotriene receptor antagonists block leukotriene receptors (e.g., montelukast), a different mechanism. Recognizing mechanisms guides selection of biologic therapy for allergic airway disease and urticaria.

A 10-year-old boy with history of peanut anaphylaxis has positive peanut sIgE of 15 kUA/L and a peanut SPT wheal 9 mm. He has not undergone oral food challenge. Which statement best describes the utility of sIgE level and SPT size?

A. sIgE and SPT definitively diagnose clinical allergy and obviate need for challenge.
B. Increasing sIgE and larger SPT size correlate with higher probability of clinical reactivity but do not alone prove reactivity; an OFC is the gold standard when diagnosis is uncertain.
C. A negative SPT excludes peanut allergy regardless of history.
D. sIgE levels are inversely correlated with the risk of anaphylaxis.

Answer: B.

Explanation: Both specific IgE levels and SPT wheal sizes correlate with probability of clinical allergy, and higher values increase the positive predictive value; however, neither alone definitively proves clinical reactivity. The oral food challenge (OFC) remains the diagnostic gold standard when history and testing are discordant or when threshold for diagnosis affects management. Negative testing with high-quality extracts and appropriate controls makes IgE-mediated allergy less likely but clinical history and DBPCFC/OFC considerations remain central. Interpretation must be individualized

Which primary immunodeficiency is classically associated with low or absent B cells, very low immunoglobulins of all isotypes, and presents in early infancy with severe infections?

A. Common variable immunodeficiency (CVID)
B. X-linked agammaglobulinemia (Bruton)
C. Hyper-IgM syndrome
D. Selective IgA deficiency

Answer: B. X-linked agammaglobulinemia (Bruton)

Explanation: X-linked agammaglobulinemia (Bruton) is caused by mutations in BTK leading to failure of B-cell maturation, absent or very low CD19+ B cells, and severely reduced serum immunoglobulins across isotypes. It typically presents in male infants after maternal IgG wanes, with recurrent bacterial infections, especially encapsulated organisms. CVID usually presents later with low IgG and variable IgA/IgM and normal/low B cells. Hyper-IgM syndromes show low IgG/IgA with normal or elevated IgM; selective IgA deficiency has isolated low IgA. Early recognition guides immunoglobulin replacement therapy.

Which hypersensitivity type best describes hemolytic transfusion reaction mediated by complement activation following preformed alloantibodies?

A. Type I
B. Type II
C. Type III
D. Type IV

Answer: B. Type II

Explanation: Type II hypersensitivity involves antibody-mediated (usually IgG or IgM) cytotoxic reactions against cell surface or extracellular matrix antigens, leading to complement activation and cell lysis. Hemolytic transfusion reactions due to preformed alloantibodies against RBC antigens are classic Type II reactions. Type I is IgE-mediated immediate hypersensitivity; Type III involves immune complex deposition; Type IV is T-cell mediated delayed hypersensitivity. Distinguishing mechanisms is key for understanding transfusion medicine and immunopathology

A patient with severe eosinophilic asthma (blood eosinophils 700 cells/µL) remains uncontrolled on high-dose ICS/LABA and triple inhaler therapy. Which biologic would be MOST targeted to directly reduce eosinophil survival by acting on IL-5 or its receptor?

A. Dupilumab
B. Omalizumab
C. Benralizumab
D. Rituximab

Answer: C. Benralizumab

Explanation: Benralizumab is an anti-IL-5 receptor α monoclonal antibody that induces antibody-dependent cell-mediated cytotoxicity of eosinophils and basophils, leading to marked eosinophil depletion. Anti-IL-5 agents like mepolizumab and reslizumab directly target IL-5; benralizumab targets the IL-5 receptor and depletes eosinophils. Dupilumab blocks IL-4Rα (IL-4/IL-13), useful for type 2 disease but not primarily reducing eosinophils via IL-5 axis. Omalizumab targets IgE; rituximab depletes CD20+ B cells and is not indicated for eosinophilic asthma. Selecting biologics depends on phenotype, biomarkers, and comorbidities.

Which diagnostic criterion is LEAST consistent with the diagnosis of common variable immunodeficiency (CVID)?

A. Marked reduction in serum IgG and IgA (± low IgM)
B. Onset of immunodeficiency symptoms in adulthood or adolescence
C. Absent B cells (CD19−) on flow cytometry
D. Poor vaccine responses to protein and polysaccharide antigens

Answer: C. Absent B cells (CD19−) on flow cytometry

Explanation: CVID is characterized by hypogammaglobulinemia (low IgG with low IgA and/or IgM), impaired vaccine responses, and recurrent infections; onset is typically in adolescence or adulthood but can vary. While B-cell abnormalities are common (e.g., reduced switched memory B cells), B cells are typically present (not absent). Absent B cells are more characteristic of agammaglobulinemia (e.g., X-linked agammaglobulinemia). Thus an absent CD19+ B-cell population argues against CVID and favors a B-cell maturation defect. Correct classification guides genetic testing and therapy.

Which of the following best describes the recommended initial management for a patient presenting to the ED with anaphylaxis?

A. Subcutaneous epinephrine 0.1 mg/kg
B. Intravenous high-dose corticosteroid bolus as first-line therapy
C. Intramuscular epinephrine 0.01 mg/kg (max 0.5 mg) into the mid-anterior thigh immediately
D. Antihistamines and observation for 24 hours

Answer: C. Intramuscular epinephrine 0.01 mg/kg (max 0.5 mg) into the mid-anterior thigh immediately

Explanation: Intramuscular epinephrine into the mid-anterior thigh at 0.01 mg/kg (up to 0.3–0.5 mg in adults) is the first-line and life-saving treatment for anaphylaxis and should be administered promptly. IV epinephrine is reserved for severe, refractory cases and requires monitored settings. Corticosteroids and antihistamines are adjunctive but not substitutes for epinephrine; corticosteroids do not act rapidly enough to treat airway/circulatory compromise, though they may help prevent biphasic reactions. Early epinephrine administration reduces morbidity and mortality.

Which HLA allele is classically associated with severe cutaneous adverse reactions (SCAR) to carbamazepine in people of certain ancestries?

A. HLA-B57:01
B. HLA-B15:02
C. HLA-DR4
D. HLA-A*02:01

Answer: B. HLA-B*15:02

Explanation: HLA-B15:02 is strongly associated with carbamazepine-induced Stevens-Johnson syndrome/toxic epidermal necrolysis in individuals of Southeast Asian ancestry, and testing is recommended in at-risk populations prior to initiating carbamazepine. HLA-B57:01 is associated with abacavir hypersensitivity. Recognizing HLA-drug associations allows pre-treatment genetic screening to prevent severe T-cell mediated adverse drug reactions. HLA associations are population-specific and guide safe prescribing.

A 45-year-old woman with severe atopic dermatitis and comorbid moderate asthma is being considered for dupilumab. What is the primary receptor target of dupilumab?

A. IL-5 receptor α
B. IL-4 receptor α subunit (blocking IL-4 and IL-13 signaling)
C. Free circulating IgE
D. TNF-α

Answer: B. IL-4 receptor α subunit (blocking IL-4 and IL-13 signaling)

Explanation: Dupilumab is a monoclonal antibody targeting the IL-4 receptor α subunit, thereby inhibiting signaling of both IL-4 and IL-13—key drivers of type 2 inflammation that underlie atopic dermatitis, some forms of asthma, and nasal polyposis. Blocking this pathway reduces skin inflammation, pruritus, and type 2 airway disease. IL-5 receptor α antagonists target eosinophils (benralizumab); anti-IgE (omalizumab) binds IgE; TNF-α inhibitors are used in other immune diseases but not for type 2 atopic disease as primary therapy. Selection depends on phenotype, comorbidities, and biomarkers.

Which statement about subcutaneous immunotherapy (SCIT) and sublingual immunotherapy (SLIT) is MOST accurate?

A. SLIT requires office administration for every dose.
B. SCIT has a stronger evidence base for long-term allergy modification for inhalant allergens, but both can be effective when used appropriately.
C. Neither SCIT nor SLIT is recommended for allergic rhinitis with asthma.
D. SCIT is contraindicated in patients on beta-blockers in all cases.

Answer: B.

Explanation: SCIT has a long evidence base demonstrating clinical efficacy and long-term disease modification for allergic rhinitis and allergic asthma when administered with appropriate extracts and schedules. SLIT has increasing evidence and is an effective alternative for certain allergens; for SLIT the first dose is typically given under medical supervision, then maintenance doses can usually be taken at home per practice parameters. Asthma controlled on medications is not an absolute contraindication; however, uncontrolled asthma is a contraindication. Use of beta-blockers increases risk with anaphylaxis and complicates epinephrine response, but beta-blockers are not an absolute, universal contraindication to SCIT—decisions must be individualized.

Which test is most specific for diagnosing Type I (IgE-mediated) hypersensitivity to a drug when evaluating immediate reactions?

A. Patch testing only
B. Drug-specific IgE (when available) and skin testing (prick/intradermal) in validated protocols
C. Basophil activation testing without correlation to history
D. Total serum IgE level

Answer: B. Drug-specific IgE (when available) and skin testing (prick/intradermal) in validated protocols

Explanation: For immediate, IgE-mediated drug reactions (e.g., penicillin), validated skin testing protocols (prick and intradermal with appropriate nonirritating concentrations) and drug-specific sIgE tests can be helpful when available. However, tests must be interpreted in the context of timing, history, and test sensitivity/specificity; negative tests may require graded challenges under controlled conditions. Basophil activation testing is useful in research and specialized centers but requires correlation. Patch testing is for delayed (type IV) reactions. Total IgE is nonspecific. Expert evaluation is often needed for drug allergy workup.

Which immune cell subset is primarily responsible for delayed-type (Type IV) hypersensitivity reactions?

A. Neutrophils
B. CD8+ and CD4+ T lymphocytes (Th1/Th17 mediated)
C. B lymphocytes producing IgG
D. Mast cells

Answer: B. CD8+ and CD4+ T lymphocytes (Th1/Th17 mediated)

Explanation: Type IV hypersensitivity is mediated by sensitized T cells (both CD4+ Th1/Th17 subtypes and CD8+ cytotoxic T cells). These T cells recognize antigen presented by APCs and secrete cytokines (e.g., IFN-γ, IL-17) that recruit macrophages and other effectors, producing tissue inflammation and delayed clinical manifestations (48–72 hours or longer). This mechanism underlies contact dermatitis, tuberculin skin test responses, and many drug-related delayed cutaneous reactions. Antibody-mediated (Type II/III) or mast cell/IgE-mediated (Type I) mechanisms are different.

In the context of allergic rhinitis, which single intervention has the strongest evidence for reducing exposure to indoor house dust mite allergens?

A. Use of HEPA air purifiers alone
B. Frequent vacuuming with standard vacuum cleaners
C. Encasing mattresses and pillows with allergen-impermeable covers plus washing bedding in hot water (>130°F) weekly
D. Monthly professional carpet shampooing

Answer: C. Encasing mattresses and pillows with allergen-impermeable covers plus washing bedding in hot water (>130°F) weekly

Explanation: For house dust mite mitigation, physical barrier encasings for mattresses/pillows and hot-water washing of bedding are practical measures with evidence of reducing mite exposure. HEPA filtration and vacuuming may help but are less effective alone; standard vacuuming can aerosolize allergens if not HEPA-equipped. Environmental control should be multi-modal and individualized—complete allergen elimination is rarely possible. Guidelines emphasize targeted, evidence-based measures such as covers and thermal washing for symptomatic patients

Which laboratory finding is most characteristic of atopic dermatitis in many patients?

A. Persistently low IgE levels and eosinopenia
B. Elevated total IgE and peripheral eosinophilia in many (but not all) patients
C. Low IgA only
D. Isolated neutrophilia

Answer: B. Elevated total IgE and peripheral eosinophilia in many (but not all) patients

Explanation: Many patients with atopic dermatitis show elevated total IgE and peripheral eosinophilia, reflecting Th2-skewed immune responses; however, normal IgE/eosinophil counts do occur. These laboratory findings are supportive but not diagnostic. The pathogenesis of atopic dermatitis involves skin barrier dysfunction, type 2 inflammation, and dysbiosis. Recognizing typical patterns supports diagnosis and selection of targeted therapies (e.g., dupilumab). Clinical phenotype guides management more than a single laboratory test.

Which of these is the most appropriate next step for a patient who on initial evaluation has suspected primary immunodeficiency with recurrent sinopulmonary infections and low IgG?

A. Begin empiric high-dose steroids.
B. Order quantitative immunoglobulins (IgG, IgA, IgM), vaccine response testing, and lymphocyte subset analysis (CD3, CD4, CD8, CD19, NK).
C. Reassure and observe—most recurrent infections in adults are viral and benign.
D. Start rituximab.

Answer: B. Order quantitative immunoglobulins (IgG, IgA, IgM), vaccine response testing, and lymphocyte subset analysis

Explanation: When primary immunodeficiency is suspected, initial workup should include quantitative immunoglobulins (IgG, IgA, IgM), assessment of specific antibody responses to vaccines (e.g., pneumococcal polysaccharide, tetanus), and lymphocyte subset analysis (CD3/CD4/CD8/CD19/NK). These tests help categorize humoral versus cellular defects and guide management, which may include immunoglobulin replacement. Empiric high-dose steroids or rituximab are not appropriate first steps. Early evaluation by an immunologist is recommended for suspected PID.

Which statement best summarizes evidence for allergen immunotherapy (AIT) in allergic asthma?

A. AIT is contraindicated in all patients with asthma.
B. Subcutaneous allergen immunotherapy has evidence for reducing symptoms and medication use in selected patients with allergic asthma when asthma is controlled, and can modify long-term disease course.
C. Sublingual immunotherapy has no role in allergic asthma.
D. AIT cures asthma in most patients within 6 months.

Answer: B.

Explanation: SCIT has RCT evidence supporting reductions in symptoms and medication requirements for allergic asthma when appropriately selected and when asthma is controlled at baseline; AIT can have disease-modifying effects over the long term. SLIT also has evidence for some allergens and may be used in selected patients. AIT is contraindicated in uncontrolled asthma due to increased risk. It is not an immediate cure and effects develop over months to years. Patient selection, safety precautions, and guideline adherence are paramount.

Which of the following best describes the mechanism of immediate hypersensitivity testing using basophil activation tests (BAT)?

A. Measures basophil degranulation (CD63 or CD203c upregulation) after exposure to suspected allergen ex vivo.
B. Detects serum complement consumption only.
C. Quantifies tissue mast cell numbers by flow cytometry.
D. Replaces skin testing as the new standard for all allergens.

Answer: A.

Explanation: Basophil activation tests measure activation markers (e.g., CD63, CD203c) on basophils after ex vivo exposure to suspected allergens, providing functional evidence of basophil responsiveness that can support diagnosis of IgE-mediated allergy. BAT can be useful when skin testing is contraindicated or when blood tests are equivocal, but it requires specialized labs and is not a universal replacement for skin testing. BAT does not measure complement or tissue mast cells directly. Interpretation requires expertise and correlation with clinical history.

Which pathogen is most commonly associated with chronic granulomatous disease (CGD) susceptibilities due to defective NADPH oxidase?

A. Streptococcus pyogenes
B. Staphylococcus aureus and catalase-positive organisms (e.g., Serratia, Nocardia, Aspergillus)
C. Influenza A virus
D. Mycoplasma pneumoniae exclusively

Answer: B. Staphylococcus aureus and catalase-positive organisms

Explanation: CGD results from defects in the phagocyte NADPH oxidase complex leading to impaired respiratory burst and decreased intracellular killing, especially of catalase-positive organisms such as Staphylococcus aureus, Serratia marcescens, Nocardia species, and Aspergillus species. These organisms can neutralize hydrogen peroxide; patients rely on their own oxidative burst for killing. CGD typically presents with recurrent abscesses, pneumonia, and granuloma formation. Diagnosis is made with dihydrorhodamine (DHR) flow cytometry or nitroblue tetrazolium testing.

A middle-aged patient develops immediate urticaria within minutes after exposure to a new biologic (monoclonal antibody). Which of the following is the MOST likely mechanism for immediate infusion-related urticaria on first exposure?

A. IgE to the biologic formed years earlier
B. Non-IgE mast cell activation (e.g., complement activation or direct mast cell activation)
C. T-cell mediated delayed hypersensitivity
D. Type III immune complex disease

Answer: B. Non-IgE mast cell activation

Explanation: Immediate infusion reactions on first exposure to monoclonal antibodies are often non–IgE-mediated mechanisms such as direct mast cell activation, complement activation-related pseudoallergy (CARPA), or cytokine release. True IgE-mediated reactions typically require prior sensitization. Delayed T-cell mediated hypersensitivity and immune-complex (Type III) reactions have different time courses. Management includes stopping infusion, supportive care, and evaluation of approach for future dosing (e.g., premedication, desensitization protocols) depending on reaction severity and mechanism

Which immunologic marker is most useful to assess for hereditary angioedema (HAE) type I/II?

A. Serum C1 inhibitor (C1-INH) level and functional assay; and low C4 level.
B. Serum tryptase elevation.
C. Elevated total IgE.
D. Anti-C1q antibodies alone.

Answer: A. Serum C1 inhibitor (C1-INH) level and functional assay; and low C4 level

Explanation: HAE types I and II are due to quantitative (type I) or functional (type II) deficiency of C1-INH; diagnostic testing includes measuring C4 (usually low), C1-INH antigenic level, and C1-INH functional assay. Type II may have normal or elevated antigenic levels but reduced function. Tryptase is for mast cell activation; total IgE is unrelated. Anti-C1q antibodies are associated with hypocomplementemic urticarial vasculitis, not HAE. Accurate testing is essential because therapies (C1-INH replacement, kallikrein inhibitors, bradykinin receptor antagonists) differ from histamine-mediated angioedema treatments.

Which of the following best explains why vaccine antibody responses (e.g., pneumococcal polysaccharide) are measured when evaluating humoral immunity?

A. They test B-cell somatic hypermutation directly.
B. They assess functional specific antibody production and memory B-cell competence beyond quantitative immunoglobulin levels.
C. They are obsolete and no longer recommended.
D. They only reflect T-cell function.

Answer: B.

Explanation: Vaccine antibody responses (e.g., to pneumococcal polysaccharide or tetanus toxoid) assess the functional ability of the immune system to mount specific humoral responses—reflecting B-cell and T-helper cell collaboration, class switching, and memory formation. These functional tests provide information beyond total immunoglobulin quantitation and can reveal impaired specific antibody production in patients with suspected humoral immunodeficiency. Choice and interpretation depend on vaccination history and timing. They are a cornerstone of PID evaluation.

Which drug is MOST commonly associated with IgE-mediated anaphylaxis in perioperative settings?

A. Midazolam
B. Neuromuscular blocking agents (e.g., succinylcholine, rocuronium)
C. Acetaminophen
D. Penicillin (rarely used perioperatively)

Answer: B. Neuromuscular blocking agents

Explanation: Neuromuscular blocking agents are among the most common causes of immediate perioperative anaphylaxis due to IgE-mediated or non-IgE mechanisms. Other perioperative triggers include antibiotics (e.g., beta-lactams), latex, and chlorhexidine. Midazolam and acetaminophen are less commonly implicated. Proper perioperative allergy evaluation includes documenting suspected agents, performing appropriate skin tests where validated, and considering alternatives for future anesthesia. Prompt recognition and treatment of anaphylaxis in the perioperative setting are critical

Which statement concerning food oral immunotherapy (OIT) for peanut allergy is MOST accurate based on recent evidence?

A. OIT permanently cures peanut allergy in nearly all patients.
B. OIT can increase the threshold of reactivity (desensitization) in many patients but requires ongoing maintenance dosing; sustained unresponsiveness after cessation occurs in a minority.
C. OIT is unsafe and therefore not used.
D. OIT is only effective when started in adults.

Answer: B.

Explanation: OIT for peanut allergy achieves desensitization in many patients—raising the threshold of reactivity and reducing risk from accidental exposures—but typically requires ongoing maintenance dosing to sustain protection. Sustained unresponsiveness (loss of clinical reactivity after stopping maintenance) is achieved in some but not most patients; long-term outcomes vary. Safety considerations include risk of allergic reactions during dose escalation and maintenance; shared decision-making, patient selection, and monitoring are essential. Guidelines reflect growing evidence and specify specialized program delivery.

Which of the following is TRUE regarding measurement of fractional exhaled nitric oxide (FeNO) in asthma management?

A. FeNO is a direct measure of airway remodeling and fibrosis.
B. Elevated FeNO suggests type 2 airway inflammation and can predict responsiveness to inhaled corticosteroids.
C. FeNO is only useful for COPD patients.
D. FeNO is decreased in eosinophilic airway inflammation.

Answer: B. Elevated FeNO suggests type 2 airway inflammation

Explanation: FeNO is a noninvasive biomarker reflecting airway epithelial inducible nitric oxide synthase expression driven by type 2 inflammation (IL-13 mediated). Elevated FeNO correlates with eosinophilic airway inflammation and predicts likely responsiveness to inhaled corticosteroids. It can aid diagnosis, assess adherence, and guide therapy in selected patients. FeNO is not a direct measure of remodeling and is not primarily used for COPD in routine practice. Interpretation should be integrated with clinical context and other biomarkers (e.g., blood eosinophils, sputum eosinophils).

Which of the following lab patterns suggests an IL-12 receptor or IFN-γ signaling defect leading to susceptibility to mycobacterial disease (MSMD)?

A. Recurrent viral infections with low NK cells.
B. Disseminated infection with nontuberculous mycobacteria or BCG after vaccination, often with impaired IFN-γ production or response.
C. Recurrent mucocutaneous candidiasis alone.
D. Isolated sinopulmonary infections with encapsulated bacteria only.

Answer: B. Disseminated infection with nontuberculous mycobacteria or BCG

Explanation: Mendelian susceptibility to mycobacterial disease (MSMD) involves defects in the IL-12/IFN-γ axis—genes encoding IL-12, IL-12Rβ1, IFN-γ receptor components, STAT1, IRF8, etc.—leading to severe or disseminated disease after exposure to weakly virulent mycobacteria (BCG, environmental mycobacteria). These patients have impaired IFN-γ production or signaling. Recognition prompts genetic testing and targeted therapies (e.g., IFN-γ in some defects) and has implications for live mycobacterial vaccines and prophylaxis.

Which of the following is the most evidence-based approach when choosing a biologic for severe type 2 asthma in 2025?

A. Choose randomly; all biologics are equally effective for every patient.
B. Individualize therapy using phenotype (e.g., allergic vs eosinophilic), biomarkers (blood eosinophils, FeNO, IgE), comorbidities (chronic rhinosinusitis with nasal polyps, atopic dermatitis), and patient goals.
C. Always start with anti-IL-5 therapy.
D. Avoid biologics unless patient is over 65.

Answer: B.

Explanation: Contemporary guidance recommends personalized biologic selection: consider phenotype (allergic IgE-mediated vs eosinophilic), biomarkers (blood eosinophils, FeNO, total and specific IgE), comorbid conditions (e.g., nasal polyposis, atopic dermatitis), safety considerations (pregnancy planning), and patient preferences (route, dosing frequency). Head-to-head comparative data are limited, and real-world and indirect comparisons guide decision-making. A precision-medicine approach maximizes benefit and cost-effectiveness. Age per se is not a universal exclusion.