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Test Code LAB4255 PROTIME (PT / INR)

Important Note

Fill tube completely to maintain correct Anticoagulant/Blood ratio

Additional Codes

Labcorp 005199

Specimen Type

Blue top tube (buffered 3.2% liquid sodium citrate) filled to the indicator with whole blood or Sodium Citrate Plasma removed from cells.

Specimen Volume

3mL Blue top (3.2% Sodium Citrate), or

5mL Blue top (3.2% Sodium Citrate), or

1mL Blue top (3.2% Sodium Citrate) MiniCollect vial, or

500uL (minimum) Sodium Citrate Plasma spun and removed from cells.

Turnaround Time

STAT: 1 hour
Routine: 4 hours

Test Schedule

Daily

Sample Stability

Test Stability at 18-24C Platelet Poor Plasma aliquot stable at -20C Platelet Poor Plasma aliquot stable at < -70C Platelet Poor Plasma Required?
PT/INR

8 hours

 2 weeks 12 months No

 

Method

Electromechanical

Reference Ranges

PT 11.6 – 14.7 seconds

INR 0.9-1.2

2.0-3.0 Usual oral anticoagulation range.

2.5-3.5 High level oral anticoagulation range.

Synonyms

Prothrombin Time; PT

CPT Codes

85610

Test Components

PT, sec; INR.

Specimen Processing

Liquid blue top tube filled to capacity. Must be performed within 24 hours of collection.

Rejection Criteria

Clotted specimens or improperly filled liquid blue top tube.

If a patients Hematocrit is >55% the coagulation tube must have the amount of anticoagulant adjusted. Call the lab for an adjusted tube. (Note: Tubes with anticoagulant adjusted must be drawn in a syringe and filled manually as the tube vacum will be compromised in the process.)

Clinical Information

The prothrombin time (PT) is a basic screening test for activity of the extrinsic coagulation pathway (factors II, V, VII, X, and fibrinogen). A prolonged PT has been observed in the following clinical disease states: congenital or acquired deficiencies of Factor II, V, VII, X, or fibrinogen. The PT may also be prolonged in liver disease, treatment with vitamin K antagonists, disorders of metabolism of vitamin K, fibrinolysis, and DIC. The PT is also used to monitor Warfarin/Coumadin therapy due to its sensitivity to variations in the concentration of the Vitamin K-dependent factors II, VII and X.

 

Because of the variations in PT results with different thromboplastin reagents and instruments, the World Health Organization (WHO) recommends that PT results be converted to an International Normalized Ratio (INR). The INR (see formula) is used to standardize PT values around the world to the WHO reference thromboplastin. The INR corresponds to the ratio of the patient’s PT and the geometric mean PT of the normal reference population raised to the ISI (International Sensitivity Index) power.

 

The ISI value of a thromboplastin reagent is provided by the manufacturer for each lot of reagent and is also contained within the barcode of the reagent for use on the STA line of Stago analyzers. The Geometric Mean is calculated from data collected for the PT reference range at Kootenai Health and must be manually entered into the instrument.