Introduction Minor head injury in older patients on warfarin may present in a variety of ways that often fall outside the remit of conventional guidelines. The aim of this study was to determine the relative risks for intracranial haemorrhage (ICH) in patients with subtherapeutic, therapeutic and supratherapeutic INR levels, in addition to the relative risks for the common symptoms at presentation.

Methods The notes were retrospectively reviewed of all patients who had a CT scan requested by the emergency department over a 2-year period (January 2008 to December 2009) and from these warfarinised head injuries were identified.

Results 82 warfarinised head injury patients were identified from 3338 requested CT scans. 12 of these patients (15%) had evidence of ICH on the CT. 72 patients had their INR checked (88%) and the RR of ICH for the INR subgroups were calculated: INR <2 (RR 1.89; 95% CI 0.65 to 5.55); INR 2–3 (RR 0.84; 95% CI 0.27 to 2.64); and INR >3 (RR 0.53; 95% CI 0.13 to 2.29). The greatest proportion of those with ICH (42%) had a subtherapeutic INR. 2 out of the 12 patients (17%) were found to have intracranial bleeding despite not meeting the criteria for a CT scan according to the NICE guidelines.

Conclusion The results of the INR subgroup analysis suggest that a subtherapeutic INR may not be protective against ICH in patients with minor head injury.