The goal is to derive and a clinical decision rule for safe exclusion of traumatic brain injury without neuroimaging in head-injured ED patients who take anticoagulant medications.

The objectives are to:

1. Derive and externally validate a new highly sensitive and maximally specific clinical decision rule for the exclusion of traumatic brain injury in head-injured ED patients who take anticoagulant medications; and,
2. Estimate the sensitivity and specificity of existing head injury clinical decision rules in head-injured ED patients who take anticoagulant medications.

This is a prospective cohort study enrolling 4000 anticoagulated patients presenting with blunt head trauma to the emergency department. Emergency physicians will record the presence or absence of clinical predictors for traumatic brain injury at the time of assessment. All patients will undergo head CT scanning and are followed for 30 days.

The adjudicated primary outcome is clinically important traumatic brain injury diagnosed at the index ED presentation. The secondary outcome is delayed clinically important traumatic brain injury, diagnosed within 30 days of normal index head CT scan.

The primary analysis will be to derive a novel clinical decision rule which excludes clinically important traumatic brain injury diagnosed at the index ED visit. The secondary analyses will include:

1. The diagnostic accuracy of existing head injury clinical decision rules in diagnosing clinically important traumatic brain injury on index ED visit, in patients who take anticoagulation; and,
2. The sensitivity and specificity of the new and existing rules for the diagnosis of both index and delayed clinically important traumatic brain injury.

Inclusion Criteria:

• Age ≥16 years
• Presents to the emergency department after a head injury
• Patient has a head CT in the emergency department
• Is a current anticoagulant user

Exclusion Criteria:

• Head injury occurred >48 h before patient's arrival to the emergency department
• Penetrating head injury
• Previously enrolled
• Patient resides outside of the hospital's catchment area
• Patient was transferred from another emergency department following neuroimaging
• Patient was not managed by the emergency or trauma physician in the emergency department
• Leaves the emergency department prior to completion of their medical assessment

The study enrolls a anticoagulated emergency department patients presenting within 48 hours of a blunt head injury.