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An audit of compliance with warfarin prescribing guidance

By Uttamlal Chouhan, MSc, MRPharmS, and Ranj Omar, MRPharmS

Woman holding warfarin tablets



To determine whether or not inpatients newly started on warfarin at Glan Clwyd Hospital, Denbighshire, had been initiated according to audit standards based on local anticoagulation guidance.



Audit standards based on local anticoagulation guidance were developed. All medical and surgical patients starting warfarin treatment were prospectively identified. Compliance with the audit standards was audited retrospectively via the patients' medical notes.

The data captured were: indication for warfarin; baseline international normalised ratio (INR) results; and adherence to local guidance relating to frequency of INR?testing and dosing.


122 patients were included in the audit, with a mean age of 74 years. The indication for warfarin was stated for 96% of the patients.

Of the group under 70 years of age and with a baseline INR <1.4, 10 out of 27 (37%) complied with the audit standards and the proportion of patients with a therapeutic INR on discharge was 90% in the group that complied and 87% in the group that did not.

Of the patients =70 years of age or with an INR?=1.4, only 33 out 95 (35%) were initiated according to the audit standards and a therapeutic INR was achieved on discharge in 68% of the group that complied and 70% in the group that did not.


This audit shows that there is considerable room for improvement in correctly following the anticoagulant guidelines for initiating warfarin therapy.



Warfarin is the most frequently prescribed anticoagulant in the UK. At Glan Clwyd Hospital, Denbighshire, as is common across the UK, the junior medical staff generally undertake warfarin prescribing for acute inpatients. Following discharge from hospital, subsequent measurement of international normalised ratio (INR) and warfarin dose adjustment is often undertaken by a patient's GP.

In 2005 the "Safer patient initiative" highlighted the importance of developing local guidance on the prescribing of warfarin. Following recommendations from the National Patient Safety Agency, local anticoagulation initiation guidance was updated to take into account both patient age and baseline INR.

In this five-month audit we sought to determine whether or not inpatients newly started on warfarin at Glan Clwyd Hospital were initiated according to audit standards based on the local anticoagulation guidance.

We found that there was considerable room for improvement — only a third of patients were initiated in compliance with the audit standards. Surprisingly, a therapeutic INR was achieved in similar proportion of patients at discharge irrespective of whether or not guidance was followed (around 90% in the younger group; around 70% in the older group). This may be explained by the small size of the entire study population, which was subsequently divided into younger and elderly groups.   

Based on the findings of this audit, the local anticoagulant guidance should be revised, in terms of the number of INR tests required, and then the updated guidance reaudited in a larger group of patients. 


Uttamlal Chouhan is principal pharmacist for clinical services and Ranj Omar was, at the time of writing, pharmacist, both in Central Area of North Wales NHS?Trust.


Citation: Clinical Pharmacist URI: 11071026

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