International Normalized Ratio Test
975 Kshs | Home Collection Available
Synonyms
International Normalized Ratio, INR
Purpose
The International Normalized Ratio (INR) Test standardizes prothrombin time (PT) results to assess how quickly your blood clots. By comparing your PT to a reference, the INR provides a consistent measure across different laboratories.
A calculated ratio derived from the patient’s prothrombin time and a reference PT, adjusted by the International Sensitivity Index (ISI) of the thromboplastin reagent.
Clinicians use the INR to monitor and adjust warfarin (Coumadin) therapy, ensuring anticoagulation stays within a safe therapeutic range (typically INR 2.0–3.0 for most indications) and minimizing risks of bleeding or thrombosis.
The test can be combined with Prothrombin Time (PT), Activated Partial Thromboplastin Time (aPTT), Platelet Count, Liver Function Tests (LFTs), and Anti–Factor Xa Levels.
Patient Preparation
The patient may need to delay the daily dose of warfarin.
Samples
2.7ml or 1.8ml-sized tube filled to 90% capacity, with a minimum volume of 90% of full draw whole blood or plasma collected in a blue top tube(sodium citrate). Evacuated collection tubes must be filled to completion and mixed immediately by inversion to ensure a proper blood to anticoagulant ratio. Store the sample at room temperature up to 24 hours, after which the sample is centrifuged and plasma frozen until ready for use.
Reference Range
0-1 month: 0.9 -1.4,>1 month: 0.9-1.2
Results Turnaround
Within 24 hours of receipt of samples.
Diseases / Diagnostic indicators
The INR test helps ensure patients on warfarin maintain safe clotting levels. The results may indicate;
Low INR (< Therapeutic Range)
- Indicates blood clots form too quickly, increasing the risk of thrombosis, deep vein thrombosis (DVT), or stroke. Clinicians may need to increase the warfarin dose.
Therapeutic INR (Typically 2.0–3.0)
- Suggests proper anticoagulation balance, minimizing both clotting and bleeding risks for conditions like atrial fibrillation or mechanical heart valves.
High INR (> Therapeutic Range)
- Indicates blood takes too long to clot, raising the risk of major bleeding, including gastrointestinal hemorrhage or intracranial bleeding. Providers may decrease the dose, hold warfarin, or administer vitamin K to reverse anticoagulation.
Regular INR monitoring guides warfarin dosing adjustments and helps prevent complications. For more on the INR test, read this study.