Prothrombin Time (PT)

Also known as: Prothrombin Time Assay, Protime, PT

Clinical Use

Use

Evaluation of the extrinsic coagulation system; aid in screening for congenital and acquired deficiencies of factors II, V, VII, X, and fibrinogen.6-8 This test is used clinically for the therapeutic monitoring of warfarin (Coumadin®) anticoagulant therapy.

Special Instructions

Not provided.

Limitations

The PT test may not detect mild deficiencies of single coagulation factors. It can be prolonged by heparin and lupus anticoagulants, potentially leading to results that do not accurately reflect anticoagulation levels. Prolonged PT results may also be seen in patients receiving anticoagulants like hirudin and argatroban. Such patients might benefit from chromogenic factor X assays to monitor warfarin effectiveness, unaffected by lupus anticoagulant or thrombin inhibitors.

Test Details

Methodology

Other

Biomarkers

International Normalized Ratio (INR)

Analyte

INR

Concentration / Level • Quantitative (Continuous) (e.g., copies/mL, % expression)

Prothrombin Time

Analyte

Prothrombin Time

Concentration / Level • Quantitative (Continuous) (e.g., copies/mL, % expression)

LOINC Codes

Order Codes

34528-0 - PT Pnl PPP

Result Codes

6301-6 - INR PPP
5902-2 - Prothrombin time

Result Turnaround Time

1 day

Specimen

Whole Blood

Volume

2.7 mL-sized tube filled to 90% capacity or 1.8 mL-sized tube filled to 90% capacity.

Minimum Volume

90% of full draw

Container

Blue-top (sodium citrate) tube; do not open tube unless plasma is to be frozen.

Collection Instructions

Collect in a blue-top tube with 3.2% sodium citrate. Tubes must be filled to capacity for proper blood-to-anticoagulant ratio. Mix by inversion at least six times. No discard tube required unless using a winged collection set.

Storage Instructions

Specimens are stable at room temperature for 24 hours. If not tested within this time, centrifuge and freeze plasma in Labcorp PP transpak frozen purple tube.