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Prothrombin Time
MessagePerformed in Coagulation
Test Code
PT
Alias/See Also
Protime
PT
INR
PT
INR
CPT Codes
85610
Preferred Specimen
3.2% sodium citrate - blue top tube
Minimum Volume
Full blue top tube or 1.0 mL plasma frozen
Instructions
The light blue capped tubes, containing 3.2% buffered sodium citrate, used for coagulation testing must be allowed to fill completely (after filling a small air space will normally be present). For patients having a hematocrit greater than 55%, contact the hospital coagulation department to obtain a special collection tube.
Reject Criteria (Eg, hemolysis? Lipemia? Thaw/Other?)
Clotted Serum received instead of Sodium Citrate plasma Specimen past stability Frozen plasma received thawed Underfilled or Overfilled, blood/anticoagulant ratio must be 9/1; specimens must be between 90% -110% full Collected in a 3.8% Sodium Citrate tube instead of 3.2% Sodium Citrate tube Drawn in outdated/expired tube HCT > 55% Hemolyzed, icteric, or lipemic sample
Setup Schedule
Monday through Sunday; Continuously
Report Available
Daily
Reference Range
System Standard (excluding WyMC)
Units of Measure = Seconds
Age Range: 0 - 150Y
PT 9.4 – 12.5
INR 0.9 - 1.1
AMR 8.0 - 150.0
Critical Range: INR >5.0
No anticoagulant Coumadin Therapy:
INR 2.0 - 3.0
Units of Measure = Seconds
Age Range: 0 - 150Y
PT 9.4 – 12.5
INR 0.9 - 1.1
AMR 8.0 - 150.0
Critical Range: INR >5.0
No anticoagulant Coumadin Therapy:
INR 2.0 - 3.0
Clinical Significance
The prothrombin time is a basic coagulation screening test for the assessment of congenital and acquired deficiencies of the extrinsic pathway (factors II, V, VII, X). The prothrombin time can be prolonged in certain clinical states, i.e. warfarin therapy, intestinal reabsorption disorders, liver failure, fibrinolysis and DIC. The prothrombin time is also used to monitor warfarin therapy because of its sensitivity to variations in the concentration of the Vitamin-K dependent factors II, VII and X. Because of the variations in the prothrombin time results with different thromboplastins and instruments, it is recommended that the prothrombin time results be converted to an INR. The INR corresponds to the value of 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 target INR is 2.5 for most conditions, including atrial fibrillation and venous thromboembolism. Higher INR values are recommended in patients with mechanical heart valve.
