A patient who has been immunized to heparin may develop an acute systemic reaction shortly after intravenous administration of heparin. The precise mechanism is unclear but it does not appear to represent anaphylaxis.


The onset is within a few minutes of an intravenous injection of heparin.


Typically the patient has a history of recent heparin therapy.


Clinical and laboratory features:

(1) chills and/or rigors

(2) fever

(3) flushing

(4) hypertension

(5) tachycardia

(6) dyspnea

(7) tachypnea

(8) feeling of chest tightness and/or chest pain

(9) nausea and/or vomiting

(10) diarrhea

(11) headache

(12) sudden drop in platelet count, which may be transient

(13) transient global amnesia

(14) cardiopulmonary arrest


Notably absent:

(1) urticaria

(2) hypotension

(3) angioedema


Differential diagnosis:

(1) pulmonary embolism

(2) anaphylaxis to another medication

(3) sepsis


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