15.4 Food Allergy, Insect Venom Hypersensitivity, Serum Sickness & Contrast Reactions

ABIM Internal Medicine Exam

Track your progress as you read

Finished sections get a check mark.

1 Chapter 0: The ABIM Exam, Blueprint & Study Strategy

0.1 Exam Format, Question Types & the 2026 Blueprint 0.2 Eligibility, Registration, Fees & Exam-Day Logistics 0.3 Scoring, the Passing Standard & Score Reports 0.4 Building a Blueprint-Weighted Study Plan

2 Chapter 1: Cardiovascular Disease (14% of Exam)

1.1 Ischemic Heart Disease & Acute Coronary Syndromes 1.2 Antithrombotic Therapy, Secondary Prevention & Mechanical Complications of MI 1.3 Atrial Fibrillation, Atrial Flutter & Stroke Prevention 1.4 Supraventricular Tachycardias, Ventricular Arrhythmias & Bradycardias 1.5 Heart Failure: Classification, Staging & Guideline-Directed Medical Therapy 1.6 Device Therapy, HFpEF & the Cardiomyopathies 1.7 Valvular Heart Disease & Endocarditis Prophylaxis 1.8 Pericardial Disease & Acute Aortic Syndromes 1.9 Hypertension: Classification, Diagnosis & Secondary Causes 1.10 Hypertensive Crises & Dyslipidemia 1.11 Adult Congenital Heart Disease & Coarctation of the Aorta 1.12 Syncope: Reflex, Orthostatic & Cardiac Causes 1.13 Cardiac Physical Examination, Murmurs & Antithrombotic Selection

3 Chapter 2: Endocrinology, Diabetes & Metabolism (9% of Exam)

2.1 Diabetes Mellitus: Diagnosis, Glycemic Targets & Pharmacotherapy 2.2 Insulin Therapy, Hyperglycemic Emergencies & Chronic Complications 2.3 Thyroid Function Testing & Hypothyroidism 2.4 Thyrotoxicosis, Thyroid Storm & Thyroid Nodules 2.5 Adrenal & Pituitary Disorders 2.6 Hypercalcemia, Hypocalcemia & Disorders of Mineral Metabolism 2.7 Osteoporosis & Paget Disease of Bone 2.8 Ovarian, Testicular & Reproductive Endocrine Disorders 2.9 Hypoglycemia, Endocrine Tumors, Polyglandular Syndromes & Severe Hypertriglyceridemia

4 Chapter 3: Gastroenterology & Hepatology (9% of Exam)

3.1 Esophageal Disease 3.2 Stomach & Duodenal Disease and Gastrointestinal Hemorrhage 3.3 Inflammatory Bowel Disease 3.4 Celiac Disease & Irritable Bowel Syndrome 3.5 Diverticular Disease & Colorectal Cancer Screening 3.6 Viral Hepatitis, Steatotic & Alcohol-Associated Liver Disease 3.7 Cirrhosis & the Complications of Portal Hypertension 3.8 Acute Pancreatitis 3.9 Chronic Pancreatitis & Biliary Tract Disease 3.10 Inherited, Autoimmune & Drug-Induced Liver Disease 3.11 Small Intestinal Disease, Ischemia & Gastrointestinal Complications of HIV

5 Chapter 4: Infectious Disease (9% of Exam)

4.1 Lower Respiratory Tract Infections & Sepsis Syndromes 4.2 Viral Respiratory Pathogens & Tuberculosis 4.3 Central Nervous System Infections 4.4 Skin, Soft Tissue, Bone & Joint Infections 4.5 Infective Endocarditis & Cardiovascular Infection 4.6 Clostridioides difficile & Catheter-Related Bloodstream Infection 4.7 HIV Diagnosis, Antiretroviral Therapy & Prevention 4.8 Opportunistic Infections & Sexually Transmitted Infections 4.9 Fever of Unknown Origin, Neutropenic Fever & Toxic Shock 4.10 Travel-Related Illness, Vector-Borne Disease & Outbreaks 4.11 Infection Prevention, Nosocomial Infection & Postexposure Prophylaxis 4.12 Rheumatic Fever, Poststreptococcal Disease, Enteric & Hepatic Infections

6 Chapter 5: Pulmonary Disease (9% of Exam)

5.1 COPD: Diagnosis, GOLD Classification & Initial Pharmacotherapy 5.2 Interventions That Reduce COPD Mortality & Exacerbation Management 5.3 Asthma: Diagnosis, Stepwise Therapy & Status Asthmaticus 5.4 Interstitial Lung Disease & Idiopathic Pulmonary Fibrosis 5.5 Sarcoidosis, Hypersensitivity Pneumonitis & Occupational Lung Disease 5.6 Pulmonary Embolism: Diagnosis, Risk Stratification & Anticoagulation 5.7 Pulmonary Hypertension & Sleep-Disordered Breathing 5.8 Acute Respiratory Distress Syndrome & Mechanical Ventilation 5.9 Pleural Disease, Empyema & Pneumothorax 5.10 Bronchiectasis, Cystic Fibrosis & Restrictive Lung Disease 5.11 Evaluation of Cough, Dyspnea, Hemoptysis & the Solitary Pulmonary Nodule

7 Chapter 6: Rheumatology & Orthopedics (9% of Exam)

6.1 Rheumatoid Arthritis: Diagnosis & Systemic Manifestations 6.2 Antirheumatic Pharmacotherapy & the Spondyloarthropathies 6.3 Gout: Pathophysiology & Acute Management 6.4 Urate-Lowering Therapy & Calcium Pyrophosphate Deposition Disease 6.5 Osteoarthritis 6.6 Systemic Lupus Erythematosus 6.7 Systemic Sclerosis, Sjogren Syndrome & Inflammatory Myopathies 6.8 The Vasculitides 6.9 Regional Musculoskeletal Syndromes, Back Pain & Sports Injuries 6.10 Other Primary Rheumatic Disorders & Mixed Connective Tissue Disease 6.11 Osteonecrosis & Metabolic Bone Disease

8 Chapter 7: Hematology (6% of Exam)

7.1 Approach to Anemia & the Microcytic Anemias 7.2 Macrocytic, Normocytic & Hemolytic Anemias 7.3 Hemoglobinopathies, Thalassemias & Paroxysmal Nocturnal Hemoglobinuria 7.4 Platelet Disorders, Thrombocytopenia & the Bleeding Patient 7.5 Coagulation Factor Disorders, Thrombophilia & Anticoagulant Reversal 7.6 Acute Leukemias, Chronic Leukemias & Myeloproliferative Neoplasms 7.7 Lymphomas & Plasma Cell Disorders 7.8 Myelodysplastic Syndrome, Myeloproliferative Neoplasms & Porphyria 7.9 Transfusion Medicine & Late Complications of Transplantation

9 Chapter 8: Medical Oncology (6% of Exam)

8.1 Breast, Lung, Colorectal & Prostate Cancer 8.2 Oncologic Emergencies 8.3 Genitourinary & Gynecologic Malignancies 8.4 Head and Neck, Bone & Soft Tissue Cancer and Cancer of Unknown Primary 8.5 Complications of Cancer & Its Treatment 8.6 Cancer Prevention, Survivorship & Psychosocial Care

10 Chapter 9: Nephrology & Urology (6% of Exam)

9.1 Acute Kidney Injury: Staging, Etiology & Urine Microscopy 9.2 Glomerular Disorders & Nephrotic Syndrome 9.3 Nephritic Syndromes, RPGN & Indications for Renal Replacement Therapy 9.4 Chronic Kidney Disease: Staging & Progression Retardation 9.5 Complications of Chronic Kidney Disease: Anemia, CKD-MBD & Acidosis 9.6 Hyponatremia, Hypernatremia & Water Balance 9.7 Potassium Disorders & Systematic Acid-Base Analysis 9.8 Renal Tubular Acidosis & Nephrolithiasis 9.9 Prostate Disorders, Urinary Incontinence & Other Urologic Conditions 9.10 Cystic Kidney Disease, Obstructive Uropathy, Tubulointerstitial Disease & Hematuria

11 Chapter 10: Neurology (4% of Exam)

10.1 Acute Ischemic Stroke: Syndromes & Reperfusion 10.2 Transient Ischemic Attack, Secondary Prevention & Hemorrhagic Stroke 10.3 Headache & Facial Pain 10.4 Seizures, Epilepsy & Movement Disorders 10.5 Multiple Sclerosis & Neuromuscular Junction Disorders 10.6 Motor Neuron Disease & Acute Peripheral Neuropathy 10.7 Cranial Neuropathies & Neuro-Ophthalmology 10.8 Peripheral Neuropathies, CNS Tumors & Other Neurologic Disorders

12 Chapter 11: Psychiatry & Behavioral Health (4% of Exam)

11.1 Major Depressive Disorder & Medical Mimics 11.2 Antidepressant Pharmacotherapy & Treatment-Resistant Depression 11.3 Bipolar Disorder, Mood Stabilizers & Lithium Toxicity 11.4 Anxiety, Stress-Related & Obsessive-Compulsive Disorders 11.5 Alcohol Use Disorder & Withdrawal 11.6 Pharmacotherapy for Alcohol & Opioid Use Disorder 11.7 Toxidromes, Psychiatric Emergencies & Suicide Risk Assessment 11.8 Psychotic, Somatic Symptom, Factitious & Personality Disorders 11.9 Eating Disorders, Sleep Disorders & Sexual Health

13 Chapter 12: Dermatology (3% of Exam)

12.1 Dermatitis, Papulosquamous & Inflammatory Dermatoses 12.2 Acne, Rosacea & Cutaneous Infections 12.3 Herpes Zoster & Autoimmune Blistering Diseases 12.4 Nodules, Tumors & Cutaneous Oncology 12.5 Dermatologic Emergencies & Severe Cutaneous Adverse Reactions 12.6 Pigment Disorders, Alopecia, Nail Disease & Photosensitivity 12.7 Vascular Dermatoses, Environmental Injury & Cutaneous Signs of Systemic Disease

14 Chapter 13: Obstetrics & Gynecology / Women's Health (3% of Exam)

13.1 Contraception, Preconception Care & Teratogenicity 13.2 Hypertensive Disorders of Pregnancy & Gestational Diabetes 13.3 Thyroid Disease & Venous Thromboembolism in Pregnancy 13.4 Menopause & Menopausal Hormone Therapy 13.5 Abnormal Uterine Bleeding, Endometrial Disease & Gynecologic Cancer Screening 13.6 Breast Disorders & Diseases of the Vulva and Vagina 13.7 Menstrual Disorders, Fibroids, Endometriosis & Early Pregnancy Complications

15 Chapter 14: Geriatric Syndromes (3% of Exam)

14.1 Comprehensive Geriatric Assessment & Frailty 14.2 Falls, Gait Assessment & Polypharmacy 14.3 Urinary Incontinence & Pressure Injuries in Older Adults 14.4 Mild Cognitive Impairment, Dementia & Its Subtypes 14.5 Delirium & the Pharmacotherapy of Cognitive Disorders 14.6 Palliative Care, Hospice & Advance Care Planning 14.7 Chronic Wounds, Nutrition, Swallowing, Constipation & Hip Fracture 14.8 Sensory Impairment, Dizziness, Elder Mistreatment & Care Settings

16 Chapter 15: Allergy & Immunology (2% of Exam)

15.1 Anaphylaxis: Recognition & Emergency Management 15.2 Urticaria & Angioedema 15.3 Drug Allergy, Desensitization & Adult Immunodeficiency 15.4 Food Allergy, Insect Venom Hypersensitivity, Serum Sickness & Contrast Reactions 15.5 Rhinitis, Conjunctivitis, Eosinophilic & Mast Cell Disorders

17 Chapter 16: Preventive Medicine, Immunization & Clinical Epidemiology

16.1 The USPSTF Framework & Evidence-Based Cancer Screening 16.2 Cardiovascular & Metabolic Screening and Primary Prevention 16.3 Adult Immunization & Vaccines in Special Populations 16.4 Clinical Epidemiology, Biostatistics & Study Design

18 Chapter 17: Miscellaneous - Ethics, Patient Safety & Quality Improvement (2% of Exam)

17.1 Principles of Bioethics & Decisional Capacity 17.2 Informed Consent, Treatment Refusal & Special Scenarios 17.3 Surrogate Decision-Making, Advance Directives & Confidentiality 17.4 Patient Safety Science, Medical Error & Diagnostic Reasoning 17.5 Quality Improvement Methods, Health Disparities & Health Equity

19 Chapter 18: Perioperative Medicine & Medical Consultation

18.1 Preoperative Cardiovascular Risk Assessment 18.2 Preoperative Pulmonary Risk & Perioperative Medication Management 18.3 Perioperative Anticoagulation, Bridging & Postoperative Complications

20 Chapter 19: Ophthalmology (1% of Exam)

19.1 The Acute Red Eye & Ophthalmic Emergencies 19.2 Painless Vision Loss & Chronic Ophthalmic Disease 19.3 Uveitis, Scleritis & Orbital Disease

21 Chapter 20: Otolaryngology & Dental Medicine (1% of Exam)

20.1 Dizziness, Vertigo & Epistaxis 20.2 Ear Disorders, Hearing Loss & Upper Respiratory Infections 20.3 Oral Cavity, Salivary Gland, Laryngeal & Taste and Smell Disorders

15.4 Food Allergy, Insect Venom Hypersensitivity, Serum Sickness & Contrast Reactions

Key Takeaways Explain This Topic AI

Food allergy is a separately named blueprint subsection under Allergy and Immunology.

Stinging insect hypersensitivity, desensitization therapy, aspirin idiosyncrasy and serum sickness are enumerated under anaphylaxis.

Venom immunotherapy reduces the risk of subsequent systemic sting reactions dramatically and is indicated after a systemic reaction in an adult.

Aspirin-exacerbated respiratory disease combines asthma, nasal polyposis and reaction to cyclooxygenase-1 inhibitors.

Most immediate reactions to iodinated contrast are non-IgE-mediated, and premedication with corticosteroids and antihistamines reduces but does not eliminate recurrence.

Last updated: August 2026

1. Food Allergy

A named blueprint subsection. True IgE-mediated food allergy must be distinguished from food intolerance , which is far more common and is not immunologic.

• IgE-mediated allergy Intolerance
• Mechanism IgE mast cell activation Enzymatic, pharmacologic, or unknown
• Onset Minutes to 2 hours Variable, often hours
• Features Urticaria, angioedema, wheeze, vomiting, hypotension Bloating, cramping, diarrhea
• Dose relationship Tiny amounts can trigger Usually dose-dependent
• Example Peanut, tree nut, shellfish Lactose intolerance

Common adult food allergens: shellfish, fish, peanut, tree nuts, and, in adults with pollen sensitization, fruits and vegetables.

Diagnosis: the history drives everything. Skin prick testing and specific IgE identify sensitization, not clinical allergy — a positive test in someone who eats the food without reaction is not an allergy, and broad panel testing generates false positives that lead to unnecessary elimination diets. Oral food challenge remains the reference standard.

Distinctive syndromes:

Pollen-food allergy syndrome (oral allergy syndrome) — itching and mild swelling of the lips and oropharynx after raw fruits or vegetables in a patient with pollen allergy, from cross-reacting heat-labile proteins. Cooked forms are tolerated , and systemic reactions are rare.

Alpha-gal syndrome — delayed anaphylaxis 3 to 6 hours after eating mammalian meat, following a tick bite (Lone Star tick in the United States). The delay is what makes it easy to miss; the patient wakes at night with urticaria and does not connect it to dinner. It also causes reactions to cetuximab and to some gelatin-containing products.

Food-dependent exercise-induced anaphylaxis — reaction only when the food (classically wheat) is followed by exercise.

Eosinophilic esophagitis — a non-IgE food-driven disorder causing dysphagia and food impaction.

Management: strict avoidance of the confirmed allergen, an epinephrine autoinjector with an action plan , education on label reading and cross-contact, and referral for consideration of oral immunotherapy where appropriate.

2. Stinging Insect Hypersensitivity

Hymenoptera — honeybee, yellow jacket, hornet, wasp, fire ant.

Classify the reaction, because it determines everything that follows:

• Reaction Description Management
• Local Swelling at the sting site Ice, analgesia

Large local Swelling over 10 cm, peaking at 24 to 48 hours Symptomatic; not a strong predictor of future systemic reaction

Systemic (anaphylaxis) Urticaria, angioedema, bronchospasm, hypotension Epinephrine ; refer for venom testing and immunotherapy

Venom immunotherapy is the single highest-yield fact here. After a systemic sting reaction in an adult, venom immunotherapy reduces the risk of a subsequent systemic reaction from roughly 30 to 60% down to a few percent, and the protection persists for years after a completed course. An adult with a systemic reaction and positive venom testing should be referred , and this is a rare instance in which a disease-modifying allergy treatment is genuinely curative.

Baseline serum tryptase should be measured in anyone with severe or hypotensive sting anaphylaxis, because an elevated level suggests clonal mast cell disease , which markedly increases risk and changes management.

3. Desensitization Therapy

An enumerated blueprint topic. Desensitization is not the same as immunotherapy.

• Drug desensitization Allergen immunotherapy
• Purpose Allow administration of a needed drug in an allergic patient Modify the underlying allergic disease

Duration of effect Temporary — lost within days of stopping the drug Long-lasting , persisting after completion

Setting Monitored, often intensive care setting Outpatient allergy clinic

Examples Penicillin in neurosyphilis or in pregnancy, aspirin in coronary disease, chemotherapy agents Venom, aeroallergens, some foods

Key point: desensitization induces temporary tolerance only while the drug is continuously present. If the drug is stopped for more than about 48 hours, the patient reverts to being allergic and must be desensitized again. Desensitization is appropriate for IgE-mediated reactions; it is contraindicated in severe delayed reactions such as Stevens-Johnson syndrome, toxic epidermal necrolysis and DRESS.

The classic indication is penicillin desensitization for syphilis in pregnancy , where no adequate alternative exists.

4. Serum Sickness

An enumerated topic and a type III immune complex reaction.

Timing: 7 to 14 days after first exposure — the delay is the diagnostic signature — or 1 to 3 days on re-exposure

Triad: fever, rash (often urticarial or a serpiginous eruption at the sides of the hands and feet), and arthralgia , with lymphadenopathy

Low complement (C3 and C4) with circulating immune complexes; proteinuria may occur

Causes: heterologous antisera and antivenoms, monoclonal antibodies, and serum-sickness-like reactions from beta-lactams (notably cefaclor ), sulfonamides, minocycline and bupropion

It is self-limited after withdrawal of the agent; NSAIDs and antihistamines suffice for mild disease, corticosteroids for severe cases. The delayed onset separates it from anaphylaxis , and low complement separates it from a simple drug exanthem.

5. Aspirin Idiosyncrasy and NSAID Hypersensitivity

An enumerated blueprint topic. Reactions to aspirin and NSAIDs are usually pharmacologic rather than immunologic , arising from cyclooxygenase-1 inhibition shunting arachidonic acid toward leukotriene production.

Aspirin-exacerbated respiratory disease (Samter triad)

The triad:

• Asthma , often severe and difficult to control
• Chronic rhinosinusitis with nasal polyposis — recurrent despite surgery

Respiratory reaction to aspirin and other COX-1 inhibitors — bronchospasm, profuse rhinorrhea and nasal congestion within 30 minutes to 3 hours

It typically develops in adulthood in someone who previously tolerated NSAIDs, which is why patients and clinicians dismiss the association.

Management: avoid COX-1 inhibitors; selective COX-2 inhibitors are generally tolerated , as is acetaminophen at standard doses. Aspirin desensitization followed by daily aspirin improves sinonasal outcomes and reduces polyp recurrence and is a recognized therapy — and it is also the pathway used when such a patient requires aspirin for coronary disease. Leukotriene-modifying drugs and biologics targeting type 2 inflammation are adjuncts.

Other NSAID reaction patterns: NSAID-exacerbated cutaneous disease in patients with chronic urticaria; NSAID-induced urticaria and angioedema in otherwise well patients; and single-NSAID IgE-mediated reactions , in which other chemically unrelated NSAIDs are tolerated.

6. Contrast-Related Allergy

An enumerated blueprint topic surrounded by persistent misconceptions.

Most immediate reactions to iodinated contrast are not IgE-mediated. They result from direct mast cell activation, and they range from urticaria to anaphylaxis-like reactions treated identically to anaphylaxis with epinephrine .

Myths worth explicitly rejecting:

Shellfish allergy does not predict contrast reaction. The historical association with iodine is not immunologically valid; shellfish allergy is to tropomyosin, and iodine is not an allergen. A patient with shellfish allergy has no more contrast risk than anyone with atopy generally.

Povidone-iodine skin reactions do not predict contrast reaction.

The true risk factor is a prior reaction to contrast itself , along with asthma and severe atopy.

Management of a patient with prior contrast reaction:

Determine whether contrast is truly necessary , and whether an alternative modality (ultrasound, non-contrast CT, MRI) would answer the question

• Use a different, low- or iso-osmolar agent where possible
• Premedicate with corticosteroids and an antihistamine on a defined schedule before the study

Recognize that premedication reduces but does not eliminate breakthrough reactions, and that resuscitation capability must be available

Delayed contrast reactions — a maculopapular eruption 1 to 7 days after administration — are T-cell mediated and are managed symptomatically.

Gadolinium carries a distinct concern: nephrogenic systemic fibrosis in advanced kidney disease, though this risk is very low with modern group II agents.

7. Allergic Complications of Transfusion

A named blueprint subsection listing hemolytic transfusion reactions, transfusion-related acute lung injury, and transfusion-related urticaria and anaphylaxis . These are covered in detail in the transfusion medicine section; the allergy-specific points are:

Isolated urticaria during transfusion is the only reaction for which the transfusion may be paused, treated with an antihistamine and cautiously resumed if symptoms resolve and no systemic features develop.

Anaphylaxis during transfusion should prompt measurement of IgA levels , because an IgA-deficient recipient with anti-IgA antibodies can react to plasma-containing products. Such patients require washed cellular products or components from IgA-deficient donors .

Any systemic feature — hypotension, bronchospasm, angioedema — means stop the transfusion and treat as anaphylaxis , not pause and resume.