Heparin‐induced acute adverse reaction – case report of a patient with acute trauma and a genetic predisposition to thrombotic events: a concurrence of events

What is known and Objective: The most common complication of heparin therapy is bleeding. Allergic reactions to heparin are rare, and the mechanisms are poorly understood. We report on a case of acute systemic reaction after subcutaneous injections of a low‐molecular‐weight heparin (LMWH) in a patient with a genetic predisposition to thrombotic events and review the literature on heparin‐induced acute adverse reaction. Case summary: A 57‐year‐old diabetic, hypertriglyceridemic and hypercholesterolemic man was admitted with a fractured right malleolus sustained while driving. He was prescribed parnaparin sodium 4250 IU subcutaneously once a day. During the third injection, the patient developed widespread pain, sickness and facial rash, followed by a state of stupor (Glasgow Coma Scale 8) and was hospitalized in Neurological Unit. He was found to be a carrier of two genetic mutations (i.e. prothrombin G20210A and MTHFR mutation) associated with an increased risk of thrombotic events. Discontinuation of parnaparin and supportive care led to a sufficient recovery of the patient to be discharged 6 days after admission. What is new and Conclusion: Treatment for heparin‐related hypersensitivity reactions is largely supportive and symptomatic. Clinicians should be aware of these rare but potentially serious adverse events. Prothrombin gene mutations are quite common, and guidelines on anticoagulant therapy for affected patients are needed.