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PT (prothrombin time) and INR
Test CodePT
Alias/See Also
Prothrombin, Protime, PT/INR, PT with INR, INR
Includes
PT, INR
Preferred Specimen
4.5 mL blood (9:1 blood to anticoagulant) in 5 ml tube
Instructions
Tube must be filled to the line to ensure the proper ratio of blood to anticoagulant.
NOTE: Collection of blood for coagulation testing through intravenous lines that have been previously flushed with heparin should be avoided, if possible. If the blood must be drawn through an indwelling catheter, possible heparin contamination and specimen dilution should be considered. When obtaining specimens from indwelling lines that may contain heparin, the line should be flushed with 5 mL of saline, and the first 5 mL of blood or 6-times the line volume (dead space volume of the catheter) be drawn off and discarded before the coagulation tube is filled. For those samples collected from a normal saline lock (capped off venous port) twice the dead space volume of the catheter and extension set should be discarded.
NOTE: Collection of blood for coagulation testing through intravenous lines that have been previously flushed with heparin should be avoided, if possible. If the blood must be drawn through an indwelling catheter, possible heparin contamination and specimen dilution should be considered. When obtaining specimens from indwelling lines that may contain heparin, the line should be flushed with 5 mL of saline, and the first 5 mL of blood or 6-times the line volume (dead space volume of the catheter) be drawn off and discarded before the coagulation tube is filled. For those samples collected from a normal saline lock (capped off venous port) twice the dead space volume of the catheter and extension set should be discarded.
Transport Container
3.2% Sodium Citrate (light blue-top)
Specimen Stability
Room temperature: 24 hours, Refrigerated: not recommended, Frozen platelet-poor plasma: 2 weeks
Reject Criteria (Eg, hemolysis? Lipemia? Thaw/Other?)
Moderate or grossly hemolyzed specimens are unacceptable.
Limitations
Many commonly administered drugs affect the results obtained in PT testing. (Example: coumadin and heparin).
Reference Range
12.5-14.8 seconds
Clinical Significance
The Prothrombin Time (PT) is a basic coagulation-screening test that is useful in the assessment of congenital and acquired extrinsic coagulation pathway deficiencies involving factors II, V, VII and X. The International Normalized Ratio (INR) is a means of standardizing therapeutic range interpretation of the PT. The use of the INR is limited to the assessment of PT in patients on oral anticoagulant therapy.
