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Nigel's surgery 92: Anticoagulant monitoring in primary care

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What should GPs take into account when monitoring and managing patients on anticoagulant medicines?

Anticoagulation (treatment to prevent blood clots) is an important intervention frequently delivered in primary care. We consider the proper and safe use of medicines, including anticoagulants, under the safe, effective and well-led key questions. The relevant key lines of enquiry (KLOEs) are:

Anticoagulation can be achieved using many different medicines. Here we consider how patients taking warfarin and the newer Direct Oral Anticoagulant (DOAC) agents are managed.

Anticoagulation is frequently prescribed to patients:

  • in atrial fibrillation
  • who have a prosthetic heart valve. (DOAC agents are not licensed in patients with prosthetic mechanical heart valves).

When prescribing anticoagulant medicines for a patient it is the responsibility of the prescriber to assure themselves that it is safe and appropriate to do so. Where prescribing and management of anticoagulants is carried out by secondary care, record this in the repeat medicines section of a patient’s record.

Managing patients taking warfarin

Patients who take warfarin need frequent monitoring to ensure that the effect is within a safe range. This is measured by the International Normalised Ratio (INR). An INR of two means that the blood takes twice as long to clot as normal blood. The target range depends upon the precise clinical indication. Patients prescribed warfarin are usually issued with and keep a 'yellow book'. This details their test results, their recommended dose and the date of their next test.

There are different models of care delivery for patients prescribed warfarin in primary care. For example:

  • Managed by the local anticoagulation service, usually based in a hospital haematology department. The patient’s practice is still responsible for prescribing the warfarin. They must make sure that appropriate monitoring and dosing advice is in place to manage the patient safely. It is good practice for this to be recorded in the patient record. For example:
    • scan the relevant entry into the yellow book or
    • upload the information from the anticoagulant clinic into the patient record.
  • A practice sends a venous blood sample to the laboratory for testing. We expect the practice to have a system in place to manage the incoming test results (see Nigel's surgery 46: Managing test results and clinical correspondence). Include results in clinical decision making, managing the patient’s warfarin dose and deciding the monitoring interval.
  • ‘Point of care” testing. Measure the INR using a blood sample from a lancet finger prick. Make sure the monitor is appropriately calibrated. The result is available almost immediately. Clinical decisions about appropriate dosing and testing intervals should be made:
    • by an appropriately experienced clinician or
    • using a computerised decision support system (CDSS), for example INRstar.

Clinician only decision making is usually carried out by a doctor, but nurses or pharmacists who can demonstrate suitable training and experience may be appropriate.

Using computerised decision support, the test is often carried out by a Health Care Assistant (HCA). The HCA must be:

  • trained to carry out this role and
  • act in line with the practice policy on managing patients who are anticoagulated. This may require all warfarin doses to be approved by a doctor, or an HCA can make a computerised dosing recommendation as long as the patient has had no change to their health, medicines, INR or recent planned doses.

All staff involved in managing an anticoagulated patient using computerised support should have had tailored, specific, role-based training.

Managing patients taking Direct Oral AntiCoagulants (DOACs)

Monitoring requirements for patients on these newer medicines is less time consuming for both patients and practices. Checks are usually required less frequently and there is no specific anticoagulant effect that needs monitoring. The correct dose must be prescribed – this depends on many factors, for example age and renal function.

There are four DOACs available to be prescribed in the UK. Each has its own specific indications and dosing information. The specific baseline and recommended periodic assessment for patients taking these medicines are detailed in the NICE CKS (Clinical Knowledge Summary) Oral Anticoagulation.

Last updated:
17 June 2019