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Coagulation

INR Test

INR standardises clotting assessment and is essential for warfarin monitoring. Including it in a health panel provides baseline coagulation and liver function information.

Doctor's Assessment Included

Reference Ranges

No established reference range

For the INR, "normal" depends entirely on whether you take an anticoagulant (a vitamin K antagonist), and we do not know that. If you do not, your INR sits around 1.0. If you do, your thrombosis service sets a target range — usually 2.0-3.0 or 2.5-3.5, and for some mechanical valves as low as 1.5-2.0. An INR of 2.5 is then exactly right, and not an abnormal result. A single reference interval would either falsely reassure one group or falsely alarm the other, so we state none. Follow the target range set by your thrombosis service.

Reference ranges may vary between laboratories. When you order a test, a BIG-registered doctor assesses your personal results in context. For treatment decisions, discuss your results with your GP.

INR: what this test measures

INR is calculated from the prothrombin time using an international sensitivity index. A normal INR is approximately 1.0. Higher values indicate slower clotting. Therapeutic range for warfarin is typically 2.0-3.0.

INR: why this value matters

INR monitoring ensures anticoagulant therapy remains in the therapeutic range — high enough to prevent clots but not so high as to cause bleeding. INR also reflects liver function since the liver produces most clotting factors.

INR: how the blood test works

Referral
No GP referral needed. After the order we arrange the referral through ZorgDomein, within one business day; orders after 17:00 or at the weekend start on the next business day. ZorgDomein emails a barcode, and that barcode is what the draw site needs.
The draw
A blood draw from a vein in the arm, at a partner laboratory's draw site. No home kit, no finger prick.
Which test
on its own €43,- Coagulation Panel · €104,- · Complete Coagulation Panel · €199,-
Where
650+ draw sites run by independent laboratories across the Netherlands. Draw sites

INR: how to prepare

  1. Preferably in the morning

    Recommended

    A morning draw makes this value easiest to compare with its reference range. Plan the draw before 10:00 if you can.

  • Water is always fine. Drink as usual beforehand, it makes the draw easier.
  • Take your usual medication, unless your own doctor told you otherwise.

INR: when is testing worthwhile?

INR is regularly monitored in patients on warfarin, before surgery, when liver disease is suspected, or as part of coagulation assessment.

INR: symptoms of a high or low value

Low Levels

A low INR (below therapeutic range in warfarin users) suggests insufficient anticoagulation and increased clotting risk. Dose adjustment may be needed.

High Levels

A high INR indicates excessive anticoagulation and increased bleeding risk. Symptoms may include easy bruising, nosebleeds, blood in urine or stool, and prolonged bleeding from minor cuts.

INR: lifestyle and this value

If on warfarin, maintain consistent vitamin K intake (green leafy vegetables), avoid sudden dietary changes, limit alcohol, inform all healthcare providers about your anticoagulant use, and attend regular INR monitoring appointments.

INR: frequently asked questions

What is a normal INR?

For people not on anticoagulants, normal INR is approximately 0.8-1.2. For warfarin therapy, the target is usually 2.0-3.0.

Why is INR monitoring important on warfarin?

Warfarin has a narrow therapeutic window. Too low and you risk clots; too high and you risk bleeding. Regular INR monitoring keeps you in the safe range.

Do DOACs require INR monitoring?

No. Direct oral anticoagulants (DOACs like rivaroxaban, apixaban) do not require routine INR monitoring.

Test Products

This marker is included in the following test panels.

Medical reviewer

Medical standards

Dr. Naimi oversees the medical standards behind our content and assessments.

Medical policy
CIBG Ministerie van Volksgezondheid,
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INR

€43,-