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:

  • Treatment of DVT or PE, including those associated with antiphospholipid syndrome or for recurrence in people no longer receiving warfarin treatment.
  • Atrial fibrillation.
  • Cardioversion (higher target values, such as an INR of 3, can be used for up to 4 weeks before the procedure to avoid cancellations due to low INR).
  • Mitral stenosis or regurgitation with atrial fibrillation, history of systemic embolism, left atrial thrombus, or enlarged left atrium.
  • Bioprosthesis in the mitral position, Bioprosthetic valve and history of systemic embolism, Bioprosthetic valve and left atrial thrombus at surgery, Bioprosthetic valves and other prothrombotic risk factors, such as atrial fibrillation and low ventricular ejection fraction.
  • Acute arterial embolism leading to embolectomy.
  • Dilated cardiomyopathy.
  • Post myocardial infarction.

A target INR of 3.5 is recommended for:

  • Recurrent DVT or PE in people currently receiving anticoagulation and with an INR above 2.

For mechanical prosthetic heart valves:

  • The recommended target INR depends on the type and location of the valve, and patient-related risk factors this varies between 2.5 and 3.5 depending on patient – related risk factor.


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.

Key Features:

  • Stable samples supplied ready to use, no pre-analytical preparation is required.
  • Panel of samples distributed over the year that spans the therapeutic target ranges.
  • Scoring based on Milan Model 3 performance specification.

1 x 0.3mL
Liquid stable biological samples suitable for use on a wide range of devices.
POCT INR Programme
AnalyteApprox. Range Covered
INR1 - 4.5Units

Related Documents


UKAS Proficiency Testing 4301UKAS Calibration 4301

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