Key takeaway: For severe anaphylaxis, boards expect prolonged observation—typically 24–48 hours—to detect biphasic recurrence, not the common “4–6 hours and home” approach used for mild cases.

Question – Anaphylaxis Discharge Timing

A 59-year-old woman is admitted to the hospital after presenting with a severe anaphylactic reaction to amlodipine. Patients who have experienced severe anaphylaxis may be discharged following an asymptomatic observation period of how many hours?

Answer Options:

A. 1–2 hours
B. 6–10 hours
C. 12–18 hours
D. 24–48 hours

Many examinees default to the familiar emergency department practice of 4–6 hours of observation after anaphylaxis, but that window applies to low-risk, mild reactions. The stem explicitly states “severe anaphylaxis,” which on the exam cues a longer, inpatient-level observation to catch biphasic recurrence that can peak hours later. Contemporary practice parameters from the American Academy of Allergy, Asthma & Immunology/American College of Allergy, Asthma & Immunology (2020) and World Allergy Organization (2020) endorse risk-stratified observation: brief (≥4–6 hours) for low-risk cases, and prolonged or admission (often 24 hours or more) for severe features or high-risk profiles.

This item tests whether you separate disposition by severity, not by a one-size-fits-all clock. Severe reactions (hypotension, hypoxia, airway compromise, need for multiple epinephrine doses) merit 24–48 hours of observation because biphasic reactions—though uncommon—cluster in the first 4–12 hours and may occur up to 48 hours. Missing this signal costs points because boards prioritize patient safety over throughput.

Why This Internal Medicine Question Is Often Missed

• Examinees overgeneralize the “observe 4–6 hours” rule and ignore the severity modifier in the stem.
• Underestimation of biphasic risk after severe reactions, especially when initial response is complete.
• Failure to apply risk factors (older age, beta-blocker use, multiple epinephrine doses, hypotension) that push toward admission-level observation.

What the Distractors Indicate

High-Yield Pearl for ABIM Exam Prep

On exam day, severe anaphylaxis = admit or observe 24–48 hours; reserve 4–6 hours only for low-risk, fully resolved reactions.

Core Learning Objectives

1. Select post-anaphylaxis observation and disposition times based on severity and risk factors.
2. Identify predictors of biphasic/refractory anaphylaxis that warrant extended observation or admission. 

The Exam Trick at Play

The stem embeds the disposition cue in the adjective “severe.” Boards reward examinees who pivot from rote time blocks to risk-stratified decisions; if you see severe features or high-risk medications, choose 24–48 hours of observation.

Additional ABIM Exam Practice Questions and Remediation

Practice Question 1 — Multiple epinephrine doses with hypotension

A 38-year-old man with peanut anaphylaxis required two IM epinephrine injections and a liter of IV fluids for hypotension. He is now asymptomatic 3 hours later. Best disposition?

Practice Question 2 — Mild reaction, single dose epinephrine, low risk

A 27-year-old woman develops generalized urticaria and throat tightness after shrimp; symptoms resolve after one IM epinephrine dose. Vitals are stable; she takes no beta-blocker. Appropriate observation time?

Practice Question 3 — Beta-blocker use

A 66-year-old man on metoprolol has anaphylaxis to IV contrast, treated with one epinephrine dose and antihistamines; he is asymptomatic at 2 hours. Best plan?

Practice Question 4 — Predictors of biphasic reaction

Which factor most strongly predicts need for prolonged observation after anaphylaxis?

Practice Question 5 — Timing of late-phase reactions

The late-phase component of anaphylaxis most often peaks and can persist for which timeframe?

Mini Case Discussion Prompt

Compare disposition plans for two patients: (1) a 25-year-old with food-triggered anaphylaxis resolved after one epinephrine dose and no comorbidities; (2) a 70-year-old on a beta-blocker with drug-triggered anaphylaxis requiring two epinephrine doses and fluids. How do severity and risk modifiers change observation time, location (ED vs ward/ICU), and discharge counseling?

Mini-FAQ Anaphylaxis Observation

• What is the minimum observation time after uncomplicated anaphylaxis?
  Many guidelines suggest at least 4–6 hours if symptoms fully resolve and no high-risk features are present; ABIM-style questions expect longer observation when severity markers exist.
• Do corticosteroids prevent biphasic anaphylaxis?
  Evidence is mixed and increasingly unfavorable; steroids should not be relied on to prevent biphasic reactions—disposition remains risk-based (AAAAI/ACAAI 2020).
• Which features mandate extended observation or admission?
  Initial hypotension, hypoxia/airway compromise, need for multiple epinephrine doses, older age, beta-blocker use, or unknown/long-acting triggers.
• When should glucagon be used?
  For refractory anaphylaxis in patients on beta-blockers with persistent hypotension or bronchospasm despite epinephrine; boards may also extend observation in these patients.

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