Allergic Reactions and Anaphylaxis: Pathophysiology Practice Questions

25 multiple-choice questions on Allergic reactions and anaphylaxis: pathophysiology for paramedic and EMT students, from Chapter 26 (Immunologic Emergencies). Read each question, pick your answer, then tap Show answer to check it and read the explanation.

25 practice questions

1. During anaphylaxis, a 64-year-old with coronary disease develops crushing chest pain and ST elevation. The most likely link is:

   1. A. Epinephrine is causing an aortic dissection
   2. B. The allergen directly damages heart muscle
   3. C. Mediators and low BP reduce coronary flow
   4. D. Hives on the chest are mimicking angina
   Show answer

   Answer: C. Mediators and low BP reduce coronary flow

   Mast-cell mediators can spasm the coronary arteries or destabilize plaque, and hypotension lowers coronary perfusion. This allergic acute coronary syndrome (Kounis syndrome) is one reason older patients with heart disease do poorly in anaphylaxis. Treat the anaphylaxis and obtain a 12-lead ECG. Dissection and direct allergen toxicity are not the mechanism.

2. A patient in shock after a wasp sting has hives, a BP of 70/40, and a heart rate of 52. You should:

   1. A. Treat it as anaphylaxis with epinephrine
   2. B. Rule out anaphylaxis because the rate is slow
   3. C. Give atropine first and hold the epinephrine
   4. D. Treat it as a simple fainting spell
   Show answer

   Answer: A. Treat it as anaphylaxis with epinephrine

   Most anaphylaxis patients are tachycardic, but some develop a slow rate from a reflex triggered by a nearly empty ventricle, or from beta blockers or heart disease. A slow pulse does not rule out anaphylaxis. With hives and hypotension after a sting, give IM epinephrine and fluids. Atropine does not treat the cause, and a vasovagal faint resolves quickly once the patient lies flat.

3. A tuberculin skin test is read 48 to 72 hours after it is placed because:

   1. A. IgE needs two days to reach the skin
   2. B. The T-cell response takes days
   3. C. The fluid takes days to absorb
   4. D. Histamine release is delayed two days
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   Answer: B. The T-cell response takes days

   The TB skin test is a type IV (delayed, cell-mediated) reaction. Sensitized T cells must travel to the site and release cytokines, so the induration peaks at 48 to 72 hours. Type I IgE and histamine reactions appear within minutes.

4. Compared with older adults, children with food-induced anaphylaxis more often present with:

   1. A. Respiratory signs rather than shock
   2. B. Shock without any breathing problems
   3. C. Chest pain from coronary spasm
   4. D. Onset delayed by several days
   Show answer

   Answer: A. Respiratory signs rather than shock

   In children, food anaphylaxis most often shows up as cough, wheeze, stridor, and vomiting; hypotension is less common and may appear late. Older adults are more likely to have cardiovascular collapse. A child with breathing signs after an allergen needs epinephrine even with a normal BP.

5. Anaphylactoid reactions differ from anaphylaxis because they:

   1. A. Are milder than true anaphylaxis
   2. B. Rarely cause any hypotension or shock
   3. C. Respond poorly to epinephrine
   4. D. Do not need prior IgE sensitization
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   Answer: D. Do not need prior IgE sensitization

   Some drugs, such as opioids and vancomycin, activate mast cells directly without IgE, so no prior sensitization is needed. The presentation can be just as severe, and the treatment is the same: epinephrine first.

6. An adult has had three episodes of hives, wheezing, and low BP in a year, and allergists have found no trigger. During her next episode, treatment should be:

   1. A. Antihistamines, since the cause is unknown
   2. B. Steroids instead of epinephrine
   3. C. Epinephrine, the same as any anaphylaxis
   4. D. Delayed until a trigger is identified
   Show answer

   Answer: C. Epinephrine, the same as any anaphylaxis

   In idiopathic anaphylaxis no trigger is found, which happens in a sizable share of adult cases. The reaction is the same, so the treatment is the same: IM epinephrine first, then supportive care. These patients should carry epinephrine auto-injectors.

7. How much intravascular fluid can shift out of the vessels in severe anaphylaxis?

   1. A. About 5% over several hours
   2. B. Up to about a third within 10 minutes
   3. C. About 10% over a full day
   4. D. Close to 90% within the first few minutes
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   Answer: B. Up to about a third within 10 minutes

   In severe anaphylaxis, mediator-driven capillary leak can move up to about 35% of the intravascular fluid into the tissues within about 10 minutes, which is why shock develops so fast and why large fluid boluses are given with epinephrine. About 5% over several hours and about 10% over a full day both understate how fast and how large the shift is. Close to 90% within minutes overstates it; a loss that large would not be survivable.

8. A teenager with cold-induced hives swims in a cold lake, then develops widespread hives, wheezing, and a BP of 72/40. You should:

   1. A. Rewarm her slowly; no drugs are needed yet
   2. B. Give oral diphenhydramine and observe
   3. C. Give IM epinephrine and begin rewarming
   4. D. Treat it as a cold-water shock reflex
   Show answer

   Answer: C. Give IM epinephrine and begin rewarming

   In cold urticaria, cold triggers mast cells. Swimming exposes the whole body, so the reaction can become systemic anaphylaxis with shock. Treat it like any anaphylaxis with IM epinephrine, and remove the trigger by drying and warming her. An antihistamine does not reverse shock.

9. Stridor in anaphylaxis indicates:

   1. A. Upper airway swelling
   2. B. Lower airway bronchospasm
   3. C. Pulmonary edema
   4. D. Pneumonia
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   Answer: A. Upper airway swelling

   Laryngeal edema can cause complete obstruction. It is an immediate threat to life.

10. Several people at one table develop flushing, headache, and a peppery taste after eating tuna that was left unrefrigerated. The likely cause is:

    1. A. A shared allergy to the tuna protein
    2. B. Histamine formed in the spoiled fish
    3. C. Mercury poisoning from the large fish
    4. D. Mass psychogenic illness
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    Answer: B. Histamine formed in the spoiled fish

    Bacteria in poorly chilled fish such as tuna and mackerel convert histidine to histamine. Eating it causes allergy-like flushing, hives, headache, and GI upset within minutes to an hour (scombroid poisoning). Several diners sharing the same fish points to a toxin rather than the same allergy. It usually responds to antihistamines, but airway or BP problems are treated like anaphylaxis.

11. GI symptoms in anaphylaxis result from:

    1. A. A bacterial toxin in contaminated food
    2. B. Low blood glucose from vomiting
    3. C. Bleeding from stomach mucosal erosions
    4. D. Gut smooth muscle spasm and edema
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    Answer: D. Gut smooth muscle spasm and edema

    Cramping, vomiting, and diarrhea are common, especially with food allergies.

12. The time from exposure to symptom onset in anaphylaxis is usually:

    1. A. Two to three days later
    2. B. One to two weeks
    3. C. Minutes to an hour
    4. D. Several months
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    Answer: C. Minutes to an hour

    The faster the onset, the more severe the reaction tends to be. Injected allergens act fastest.

13. Which feature of the first reaction most raises the risk that anaphylaxis will return hours later?

    1. A. Hives that cleared within minutes
    2. B. Needing more than one epinephrine dose
    3. C. A reaction to a food rather than a drug
    4. D. Itching that began before the hives
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    Answer: B. Needing more than one epinephrine dose

    Biphasic reactions are more likely after a severe first phase, especially one that needed more than one dose of epinephrine or caused hypotension. These patients warrant longer observation. A quick response to treatment is reassuring, and the type of trigger or the order of skin symptoms is not a reliable predictor.

14. Patients at risk of anaphylaxis are told to carry two epinephrine auto-injectors because:

    1. A. One device commonly misfires in use
    2. B. Each device delivers about half a dose
    3. C. The first dose is just a test dose
    4. D. Some reactions need a second dose
    Show answer

    Answer: D. Some reactions need a second dose

    A meaningful minority of anaphylaxis patients need more than one dose of epinephrine before help arrives, especially with severe reactions or long transport times. Device failures are uncommon, each device holds a full dose, and there is no test dose.

15. Which route of allergen exposure usually causes the fastest, most severe reaction?

    1. A. Injection
    2. B. Skin contact
    3. C. Ingestion
    4. D. Inhalation of pollen
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    Answer: A. Injection

    Injected allergens, such as IV drugs and insect venom, reach the circulation immediately.

16. Which patients are at greatest risk of fatal anaphylaxis?

    1. A. Those with hay fever
    2. B. Those with asthma
    3. C. Those with past mild hives
    4. D. Those with diabetes
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    Answer: B. Those with asthma

    Asthma raises the risk of fatal respiratory compromise. Delayed epinephrine is the other major risk factor. Hay fever and past mild hives are common in allergic patients but do not predict a fatal reaction the way asthma does.

17. A patient with mastocytosis, a disorder with too many mast cells, is stung by a wasp. Compared with other patients, she is at higher risk of:

    1. A. A purely local reaction at the sting site
    2. B. Delayed contact dermatitis around the sting
    3. C. Serum sickness within the first few hours
    4. D. Severe and rapidly progressing anaphylaxis
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    Answer: D. Severe and rapidly progressing anaphylaxis

    Mastocytosis means more mast cells to release mediators, and sting anaphylaxis in these patients is often severe, with hypotension and sometimes no hives. They should carry epinephrine. Contact dermatitis and serum sickness are delayed reactions.

18. The tachycardia seen in anaphylaxis is mainly a response to:

    1. A. Direct damage to the heart muscle
    2. B. Fever from a secondary infection
    3. C. Vasodilation and low BP
    4. D. Excess thyroid hormone release
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    Answer: C. Vasodilation and low BP

    The heart speeds up to compensate for falling blood pressure.

19. Cardiac arrest in anaphylaxis is most often caused by:

    1. A. Airway obstruction or shock
    2. B. A primary heart attack (MI)
    3. C. Severe hyperkalemia
    4. D. Profound hypoglycemia
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    Answer: A. Airway obstruction or shock

    Treat the airway aggressively and give epinephrine and fluids early.

20. A localized allergic reaction is limited to:

    1. A. Multiple body systems
    2. B. The airway and lungs
    3. C. The cardiovascular system
    4. D. The area of contact
    Show answer

    Answer: D. The area of contact

    Local swelling around a sting, without systemic signs, is not anaphylaxis but should be watched.

21. Large local reactions to insect stings:

    1. A. Usually lead to systemic anaphylaxis
    2. B. Require intubation
    3. C. Rarely progress to anaphylaxis
    4. D. Cause shock in most cases
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    Answer: C. Rarely progress to anaphylaxis

    Swelling can be impressive but usually stays local. Watch for systemic signs.

22. Serum sickness is a delayed reaction that causes:

    1. A. Immediate airway swelling
    2. B. Fever, rash, joint pain
    3. C. Hypoglycemia
    4. D. Sudden, isolated bronchospasm
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    Answer: B. Fever, rash, joint pain

    It is a type III reaction appearing 1 to 2 weeks after exposure to drugs or antiserum.

23. A man who had anaphylaxis to yellow jacket stings asks how to lower his risk from future stings. Allergists can offer:

    1. A. Venom allergy shots (immunotherapy)
    2. B. A daily antihistamine for the rest of his life
    3. C. A yearly course of oral prednisone
    4. D. A tetanus booster after each sting
    Show answer

    Answer: A. Venom allergy shots (immunotherapy)

    Venom immunotherapy gradually desensitizes the immune system and lowers the risk of another systemic sting reaction to about 5% or less in most patients. Antihistamines and steroids do not prevent anaphylaxis, and he must still carry epinephrine.

24. Tryptase is a marker that may be measured in the hospital to confirm:

    1. A. Mast cell activation
    2. B. Myocardial infarction
    3. C. Kidney failure
    4. D. Liver damage
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    Answer: A. Mast cell activation

    Tryptase rises after anaphylaxis and helps confirm the diagnosis.

25. Exercise-induced anaphylaxis is often associated with:

    1. A. Cold-water swimming right after a meal
    2. B. Certain foods eaten before exercise
    3. C. Drinking large amounts of water
    4. D. Wearing tight elastic clothing
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    Answer: B. Certain foods eaten before exercise

    Some patients react only when food (often wheat) is followed by exercise.