Warfarin dosing error - medical case study

Even the best systems require constant checking and reviewing, especially with INR and warfarin, to ensure that they 'fail safe' and not 'unsafe'...

  • Date: 01 April 2007

BACKGROUND: A patient at a general practice, Mrs W, was receiving warfarin and staff were monitoring the INR and adjusting the dosages on the basis of a detailed programme implemented after consultation with the local haematology department. The practice nurses kept a book of results and warfarin doses and adjusted the dose as the results were received.

A result for Mrs W was received by the practice and seen by a practice nurse who was not the one who had taken the sample. This led to a delay in checking the result and dosage. It was realised that the INR result was abnormally high. The nurse who had taken the sample tried to contact Mrs W by phone to tell her to alter her dose but had no success. She then left a message on an answering machine to contact the surgery. When there was no contact from the patient a letter was sent to ask her to contact the surgery and again it elicited no response. Relatives found Mrs W had collapsed and died, alone in the house. She had suffered a pontine intracranial haemorrhage, probably while the practice was attempting to contact her.

ANALYSIS/OUTCOME: The practice immediately reviewed its method of recording samples taken, results handling and calculation of dosages. They also drew up a firmer policy on contacting patients and relatives in the event of an abnormal result. They realised that they needed to be more active in making such contacts. They completely revamped their system, again in consultation with local laboratory.

The practice was very well run and the staff were devastated that the patient had died, but even the best systems require constant checking and reviewing, especially with INR and warfarin, to ensure that they 'fail safe' and not 'unsafe'.

A claim was raised on behalf of the family which was quickly settled for a sum of £60,000.


  • Ensure you have an effective results-handling process.
    Make sure systems 'fail safe'.
  • Ensure patients are contacted with dose changes, especially warfarin.
  • Ensure careful sharing of responsibility for tests and results handling.

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