The CT scan is normal, but no test is 100% sensitive for pathology. Head CTs are not infrequently falsely negative early on in stroke and can be falsely negative in head injury as well. This is especially relevant in patients who are taking anticoagulants. Management options in this case include discharge with good return precautions, 6 hours of observation in the emergency department with possible repeat head CT, admission for observation, and/or empiric warfarin reversal.


Anticoagulation with oral anticoagulants (OACs), such as warfarin or one of the newer agents mentioned in Table 1, increases the risk of an intracranial bleed (ICB) after minor blunt head trauma. The early risk is about 5%, so all patients with significant head trauma and use of an OAC should have a stat head CT regardless of whether there is loss of consciousness or other another red flag is present. 

What is frequently underappreciated is that the risk of a delayed ICB is estimated to be between 0.6% and 6%, which is approximately 40 times higher than for a patient who is not taking an OAC. This bleeding often presents 6 to 24 hours after the initial injury. The mechanism is likely that the initial platelet plug (primary hemostasis) occurs normally because platelet function is normal, but stabilization of the clot with fibrin (secondary hemostasis) is impaired. Because of this risk for delayed ICB, there have been recommendations that patients taking an anticoagulant be observed for 6 hours in the emergency department with consideration for a repeat head CT if any clinical parameters, even an increasing headache, worsen.

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Some experts even go so far as to recommend routine admission and/or OAC reversal in the setting of a negative head CT. Treatment should probably be individualized by considering the risk of bleeding based on mechanism of injury, examination, and INR against the risk of stroke or pulmonary embolism from short-term reversal of an OAC for a few days. See Table 1 for more details and information on minor head trauma with other medications that can increase the risk of bleeding.

Case outcome

This patient went home. He did not answer the door when the neighbor came over the next morning, so 911 was called. On arrival to the emergency department, the patient was deeply comatose. He was intubated, and a repeat CT scan showed a huge subdural hematoma. Because of the grim prognosis, supportive care was withdrawn and the patient died.

Table 1. Blood thinners and head trauma

Anti-Clot (warfarin/dabigatran etexilate/apixaban/rivaroxaban/edoxaban): Early bleed risk ~5%. Late bleed risk 0.6% to 6%
Red flags Lives alone, night time, <6h from injury, amnesia/loss of consciousness, INR >2.5, concerning mechanism, older age, altered mental status, large scalp swelling seen on exam or CT, skull fracture, persistent vomiting
CT (+) Factor IX, fresh frozen plasma (FFP), vitamin K >surgery. More aggressive if mass effect or higher INR. (Transfer)
CT (-) Observe 4 to 6 hours and consider repeat head CT if worse or multiple red flags (above)
Reversal If bad mechanism, still consider FFP to reverse and/or vitamin K, even if CT negative. In a survey of trauma surgeons by Coimbra, 74% of respondents reverse warfarin.
Disposition Controversial: some authors advise 24h admit for all; others advise discharge home for most
Anti-Platelet (clopidogrel/ticagrelor/prasugrel): Early bleed risk ~12%. Late bleed risk is minimal.
CT (+) Platelet transfusion and admit or transfer to trauma center
CT (-) Most can be discharged without need for observation or repeat head CT
Others Much lower risk than above: aspirin >ginkgo/ginseng/garlic/ginger, vitamin E >SSRIs

Brady Pregerson, MD, is an emergency physician at Cedars-Sinai Medical Center in Los Angeles and at Tri-City Medical Center in Oceanside, California.


  1. Pregerson B. Quick Essentials: Emergency Medicine: The One-Minute Consult—Version 4.0.; 2010.