Specimen Collection

Citrated platelet poor plasma. Minimum volume 0.5 mL.

2.7 mL Adult Citrate Blood

or

1.8 mL Citrate Blood

or

1 mL Paediatric Micro-citrate Blood

• Tube must be adequately filled.

Reference Intervals

Uncertainty of Measurement : 4%

Therapeutic - Units: Units

Age Range	Either Sex
All	2 - 3

Turnaround Time: Within 2 hours
Diagnostic Use and Interpretation

• The INR is used for the monitoring of warfarin therapy only.
• Whole blood Interrnational Normalised Ratio (INR) is available for paediatric patients for warfarin monitoring only. Please arrange this with phlebotomy (ext 29269) if this service is required.
  

The INR pertains only to those patients who are receiving Warfarin or other oral anticoagulants and for up to three days after discontinuation of therapy. Because different thromboplastins have markedly different sensitivities to the coagulation defect induced by oral anticoagulants the ISI (International Standardised Index) is used to equate the different reagents. Use of the ISI allows "correction" of the PR obtained to give standardised reporting throughout the world.

Interpretation

The desired range for INR depends on the underlying pathology

e.g.

post VTE	2.0
mechanical valve	2.5 - 3.0
lupus anticoagulant	2.0 - 3.0

• Excessive INR response is commonly due to subclinical vitamin K deficiency, e.g. poor diet in the elderly, antibiotic therapy.
• The response is more predictable with small doses of vitamin K (0.5 - 1.0 mg)
• Also consider drug interaction.

See

Prothrombin Ratio

Contact Information

For further information contact the Haematology laboratory (Ext 22067) or:

Dr Nicola Eaddy	Ext 22005
Dr Peter Bradbeer	Ext 22062
Dr Anna Ruskova	Ext 22137
Dr Nikhil Rabade	Ext 22071

Last updated at 13:09:28 11/09/2024