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CoaguChek test strip calibration issue

A message from Dr Jo Scott-Jones, Pinnacle MHN medical director.

You may be aware of a concern raised about the accuracy of point of care testing for the International Normalised Ratio (INR). We have explored this with Dr Alan Neal from Pathlab and he has been extremely helpful, including obtaining a review of the issues and advice from haematologist Dr Paul Harper. 

The issue only affects certain "chip lot codes" of test strips and only if readings are greater than 4.5. 

The advice from Dr Harper is well articulated in the following patient scenarios.

  • If you have a patient who has been stable long-term, has the occasional INR above 3.0 (target 2.0 to 3.0) in the past and their latest INR is marginally above 3.0, I would manage as normal.
  • ¬∑If you have a patient who has been stable long-term with a target INR of 2.5 to 3.5 and they are still within range, I would manage as normal.
  • If you have a patient with an INR unexpectedly high (between 3.5 and 4.0) and there is no obvious cause, your usual approach would be to consider a dose reduction. I would suggest you do just the same. If the test-strip is reading a little high the patient is still going to be above the therapeutic range and a minor dose change would be safe.
  • If you have a patient with an INR >4.0, you are going to either withhold treatment or make a dose change. This advice would not change.
  • The only situation where there could be concern with the test-strip measuring slightly high is in the patient with an INR just above the therapeutic range. In this situation there is the potential to reduce the dose unnecessarily. Remember that the risk of bleeding from warfarin is low until the INR is >4.0, therefore running a slightly high INR for a short period is not a significant risk.

This situation is continuing to be monitored and we will update you with any changes to this recommendation. We understand Canterbury Laboratories have taken another approach and have given clinicians in Canterbury advice to "double check" all point of care INR results >3.0. Pinnacle MHN, Medsafe, and Pathlab are happy with the above advice which reflects the issues raised by the manufacturer. 

For further information, this letter from Dr Paul Harper summarises the current situation, any risks and appropriate management as well as an updated recall document from Roche Diagnostics which includes clarifications around comparison measurements. For more information contact Dr Jo Scott-Jones, Pinnacle MHN medical director. 

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