Pathology Handbook

INR (Warfarin Monitoring)

Synonyms

INR, Prothrombin ratio, Warfarin level, Warfarin monitoring

Clinical Indications

Monitoring of oral anticoagulant therapy.

For advice on warfarin dosing and induction see Guidelines on the use of Oral Anticoagulants.

Request Form 

Request via ICE

Availability

Daily

Specific Criteria

Patient should be bled with minimal stasis

Patient Preparation

Patient should ideally be at rest

Turnaround Time

Same day.

Specimen

Fresh citrated Blood; sample must be received by the laboratory within 4 hours of collection.

Volume

4.5 ml

Container

Blue capped vacutainer tube

Vacutainer blue top

Collection

Clean venepuncture. Samples must be received by the laboratory within 4 hours of collection.

Causes for Rejection

Underfilled, clotted, haemolysed or if sample is too old.

Reference Range

Patients not on oral anticoagulants: 0.8 - 1.2
For patients on treatment the therapeutic range varies by case.