Prothrombin Time

Label Mnemonic:	PT
Epic code:	LAB320
Order form:	Laboratory Requisition
Supply order:	Supply Order Form
Billing:	Billing Policies
CPT code:	85610

Specimen(s):

Plasma More information

Collection Medium:

Light Blue top tube 1.8 mL (Na Citrate)

Minimum:

Full draw; 1.8 mL light blue top (mix well). Tube must be at least 90% full.

Rejection Criteria:

Short drawn tube, clot, traumatic tap (excessive hemolysis).

Turn Around Time:

1 hour (upon receipt in laboratory)

Reference Range:

9-12 seconds

INR Critical Reference Value: greater than 3.9

Comments:

The INR corresponding to the PT is reported to assist in the monitoring of oral anticoagulants. Must be drawn swiftly with a clean venipuncture (no hematoma). Time drawn must be indicated on requisition. A PT can be performed on a sample if it is kept unopened and uncentrifuged at room temperature to be delivered to lab within 12 hours. A special tube from the lab is necessary if the hematocrit is over 55%.

Prothrombin Time may be performed on the same collection tube as Activated Partial Thromboplastin time (aPTT) and Fibrinogen.

INR values are intended to be used for patients receiving oral anticoagulant therapy with warfarin. A patient's target INR range may depend on multiple factors, including the clinical indication for anticoagulation and bleeding risk. A standard intensity warfarin therapeutic INR range is 2.0 to 3.0.

Methodology:

Optical clot detection.

Sample Processing:

Double-centrifuge specimen to prepare platelet-free plasma.
Immediately centrifuge specimen at 3500 RPM for 12 minutes.
Using a plastic transfer pipette, carefully remove plasma from cells avoiding the platelet/buffy coat.
Place plasma into a labeled plastic tube.
Centrifuge plasma again at 3500 RPM for 12 minutes.
Remove the top of the plasma and place into a labeled plastic tube.
Freeze double-spun plasma within 4 hours of collection time at -20 degrees C or below.

Sample Storage:

Freeze plasma immediately.

Transport Instructions:

Place labeled specimen into zip-lock type biohazard bag; seal bag.
Place requisition into outside pocket of bag.
Place dry ice on top of specimen in Styrofoam container to maintain frozen temperature.
Samples received thawed will be cancelled.

See also:
Activated Partial Thromboplastin Time (aPTT), Plasma

See Additional Information:
Hematology Critical Lab Values
International Normalized Ratio (INR)
Hemolysis Chart
Phlebotomy Tubes and Order of Draw