Prothrombin Time (PT)

Casandra

Casandra Test Code LC96088Version 1 (DRAFT)

Performing Lab

Lab LabcorpLab Test ID 005199CPT Code 85610

Prothrombin Time (PT)

Also known as: Prothrombin Time Assay, Protime, PT

Clinical Use

Order Test

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

Values obtained with different assay methods should not be used interchangeably in serial testing. Consistent use of one assay method is recommended for monitoring each patient's therapy. If serial monitoring is needed, order the serial monitoring test, 485199. Hematocrits above 55% require adjustment of the citrate volume in the collection tube. Specific collection instructions are available in the Coagulation Collection Procedures guide.

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

Result Codes

6301-6
5902-2

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.