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Patients receiving warfarin, a Vitamin K antagonist (VKA) as anticoagulant therapy will have their International normalized ratio (INR) measured regularly to ensure that their medication is effective, and the dose adjusted accordingly to maintain the INR within the appropriate range. Warfarin, the most commonly used VKA, is a coumarin derivative that acts by inhibiting vitamin K dependent clotting factors (II, VII, IX, X) in addition to the anticoagulant proteins C and S. The INR calculation is based on a standardised ratio of the patient’s Prothrombin time, (PT) versus a normal control sample. Therefore, the INR of a healthy individual not on anticoagulation therapy would be 1.0.
PT measures the time taken (in seconds) for the blood to clot following addition of thromboplastin, an activating enzyme. Warfarin is licensed for prophylaxis of embolization in rheumatic heart disease and atrial fibrillation, prophylaxis after insertion of prosthetic heart valve, prophylaxis and treatment of venous thrombosis (DVT), pulmonary embolism (PE), and in transient ischaemic attacks.
A target INR of 2.5 is recommended for:
A target INR of 3.5 is recommended for:
For mechanical prosthetic heart valves:
This test may occasionally be used on a patient not taking anticoagulant medicine to check for a bleeding disorder, liver disease, Vitamin K deficiency or to ensure clotting ability before surgery.
The INR EQA control material is suitable for use with the majority of POCT devices including the Abbott-i-STAT, the Roche CoaguChek range of devices, and the Siemens Xprecia Stride. The material is supplied in a ready to use vial, no prior treatment is required to activate the product.
The programme includes a panel of samples spanning the pathological range, however the majority of samples distributed in the year are specifically selected to challenge the therapeutic targets of 2.5 and 3.5. One liquid stable sample is distributed every 2 months, a minimum of six samples per year, some of which are distributed on a number of occasions. This allows for the assessment of the organisation’s and method’s performance, including linearity, bias, within and between batch imprecision.
|POCT INR Programme|
|Analyte||Approx. Range Covered|
|INR||1 - 4.5||Units|