Laboratory Test Information Guide

Details for INR

Test Name: INR
Alternate Name(s): International Normalized Ratio
Prothrombin Time
Laboratory: Core
Specimen Type: 2.7 mL Blue (3.2% Sodium Citrate) top Vacutainer

0 months-10 years: 1.8 or 1 mL Blue top (3.2% Sodium Citrate) tube
Collection Information: Tubes must be filled until vacuum exhausts (until the fill line marked on tube).
Both INR and PTT can be performed on one Blue top tube.
Sample Stability:
Patients not anticoagulated or on warfarin only - ideally, samples should be spun and tested within 4 hours of collection. In the case of an unavoidable delay, INR results ONLY may be reported up to 24 hours after collection.

Set the centrifuge temperature to 19 oC.

Centrifuge at 3000 rpm for 10 minutes at 18 - 20 oC Also the samples should be put on to the instrument at 18 - 20 oC.

Do not use the cold block on the coagulation bench.
Test Schedule: As required
Turnaround time from when specimen
is received in testing laboratory:
4 hours
1 hour
Reference Range: Age/Range:
< 5 days:
5 days-Adult:
Effective Date: 2011-01-14
Revised Date: 2020-12-29
Critical Value: INR: ≥ 4.5
Interpretive Comments: Detects abnormalities in the extrinsic pathway. Increased in liver disease, Vitamin K deficiency, obstructive jaundice and hemorrhagic disease of the newborn.
Special Processing:  
Comments: PT results will not be released on patients. For the INR based Maddrey Score please use the following link:
Maddrey Score.
This score is based on ISI and PT control values. Please use current ISI of 1.1 and PT control of 11.7 seconds. These values will be updated when necessary.
Use MELD score as alternative.
Method of Analysis: Optical clot detection
Critical Information Required: Anticoagulant therapy
Storage & Shipment: Blue (Sodium Citrate) top specimens are kept at 18-24 degrees Celsius.

Blue (Sodium Citrate) top specimens should be centrifuged and tested within 24 hours of specimen collection.

Samples are discarded after 24 hours.
System Codes: 
INR or
Referred To:  

Questions? Comments? Contact Laura Gopaul