Prothrombin Time with INR

Clinical Significance

Prothrombin Time with INR - Screening test for abnormalities of coagulation factors that are involved in the extrinsic pathway. Also used to monitor effects of Warfarin therapy and to study patients with hereditary and acquired clotting disorders.

Clinical Significance

Prothrombin Time with INR - Screening test for abnormalities of coagulation factors that are involved in the extrinsic pathway. Also used to monitor effects of Warfarin therapy and to study patients with hereditary and acquired clotting disorders.

Test Details

Methodology

Photo-Optical Clot Detection

Reference Range(s)

INR

≤3 months

Not established

>3 months

Reference range

0.9-1.1

Moderate-intensity Warfarin therapy

2.0-3.0

Higher-intensity Warfarin therapy

3.0-4.0

PT

≤3 months

Not established

>3 months

9.0-11.5 sec

Flagging not provided. Pediatric reference intervals have not been established. Based on published literature, the adult reference interval (9.0-11.5 seconds) is generally applicable down to approximately 3 months of age with younger patients having a slightly higher upper limit by several seconds. Warfarin Therapeutic INR Range: 2.0 - 3.0

Alternative Name(s)

PT

Preferred Specimen(s)

One full unopened 3.2% sodium citrate (light blue-top) tube

Alternative Specimen(s)

1 mL frozen plasma: If the specimen will be delayed longer than 48 hours, centrifuge specimen for 15 minutes at 2500-3500 rpm. Using a plastic pipette, remove plasma, taking care to avoid the WBC/platelet (buffy) layer and place into a transport tube and freeze at -20° C. Ship on dry ice.

Minimum Volume

Ratio of blood to citrate is critical. Submit difficult draws in pediatric (light blue-top) tube
0.5 mL frozen plasma

Collection Instructions

A completely filled tube is necessary because the correct ratio of blood to citrate is critical (9:1).
Mix by gentle inversion 3-4 times. Do not uncap.

Transport Container

3.2% sodium citrate (light blue-top) tube

Transport Temperature

Room temperature

Specimen Stability

Unopened light blue-top tube
Room temperature: 48 hours
Refrigerated: Unacceptable
Frozen: Unacceptable
Separated platelet-poor plasma
Room temperature: Unacceptable
Refrigerated: Unacceptable
Frozen: 14 days

Reject Criteria

Gross hemolysis • Grossly lipemic • Improper blood to citrate ratio • High hematocrit • Improper blood collection

Setup Schedule

Set up: Mon-Sat (All shifts), Sun: STAT ONLY; Report available: 1 day