Why do electronic health records reveal oral anticoagulant prescription after haemorrhagic stroke?

Oral anticoagulation (OAC) is used to prevent stroke in patients with atrial fibrillation or heart valve disorders. However, OAC may cause haemorrhagic stroke. We completed a randomized trial of stroke secondary prevention 1, using primary care electronic health records (EHRs) collected into the UK Clinical Practice Research Datalink (CPRD). A small proportion of participants were prescribed warfarin following a haemorrhagic stroke diagnosis. The present research aimed to explain this observation. Participants were selected from all 11 391 patients with prevalent stroke, from 106 family practices in England and Scotland, included in the trial 1. Patients were included if they had a record of haemorrhagic stroke before the trial and were treated with warfarin during the trial. Family physicians were sent a postal questionnaire asking respondents about the nature of the stroke suffered by the patient and indications for warfarin therapy. Type of stroke was coded using the International Classification of Diseases 10th Revision 2. Warfarin accounts for 99% of OAC prescriptions in the CPRD. The project was approved by an external scientific and ethical review committee (ISAC protocol 08_083A2). GPs consented to their practice's participation. Fully anonymized data were used and no patient consent was sought. There were 134 (1.2%) participants with EHRs documenting previous haemorrhagic stroke who were prescribed warfarin during the trial. The index stroke event was coded into the EHR as a sub-arachnoid haemorrhage for 25 (24%) of cases and as intracerebral haemorrhage (ICH) for 78 (76%) of cases. There were 40 (47%) women and the mean age was 75 years (range 40 to 94 years). Questionnaire responses were obtained for 103 (77%) patients with sufficient information to confirm the type of stroke obtained for 86 (64%) (Figure 1). Figure 1 Flow chart showing physician-reported data for confirmed stroke type and indication for OAC therapy in 103 participants with electronic records for haemorrhagic stroke Questionnaire responses revealed that there were 41 (48%) patients with a physician-confirmed diagnosis of cerebral infarction (n = 39) or other non-haemorrhagic stroke (n = 2). The diagnosis was confirmed by imaging reports recorded for 36 (88%) of patients. There were five patients with a code for ischaemic stroke recorded after the initial haemorrhagic stroke but only two of these were within 1 year of the index stroke, possibly representing a clarification of the initial diagnosis. Indications for OAC in this group of participants included atrial fibrillation (n = 27), disease of pre-cerebral and cerebral arteries (n = 4), venous thromboembolism and other and not known (n = 10). There were 45 patients with a physician-confirmed diagnosis of haemorrhagic stroke including sub-arachnoid haemorrhage (n = 17) and ICH (n = 28). The diagnosis was supported by imaging results for 38 (84%) patients. Indications for OAC therapy included atrial fibrillation (n = 20), venous thrombosis (n = 10), pulmonary embolism (n = 5), aortic valve replacement (n = 3), percutaneous coronary intervention, vasculitis and not known (n = 7). We conclude that in the EHRs of a large population of stroke patients, there may be appreciable numbers with a diagnosis of haemorrhagic stroke who are treated with OAC therapy. We reported previously on the clinical coding of stroke in EHRs 3 and the potential for misclassification of stroke diagnoses. The present results should not be considered to evaluate the overall reliability of stroke coding in EHRs, because the sample was one in which data discrepancies were expected. In about half of patients, the stroke event was mis-coded as a haemorrhagic stroke when the physician-reported diagnosis for the same event date was one of cerebral infarction. Misclassification might sometimes result from haemorrhagic transformation, which is not necessarily a contra-indication to OAC therapy. Physicians may draw on sources of data from outside the EHR. Nevertheless, it is concerning that appreciable numbers of stroke patients are prescribed OAC therapy with incorrect diagnostic information coded into their EHRs, with potential medico-legal implications. Improved information sharing between providers would be of benefit to physicians. A second group comprises patients with a confirmed diagnosis of haemorrhagic stroke who were treated with OAC therapy for co-existing thromboembolic disorders. This highlights the difficult balance of risks and benefits that may sometimes be required in clinical practice. However, the use of OAC therapy in patients with previous ICH remains controversial 4. Improved evidence and decision support are required for these high risk patients.