II. Background
- Evaluates the Extrinsic Clotting Pathway
- Plasma collected in a tube containing citrate, which binds Calcium and prevents initial clotting
- Both Calcium and Tissue Thromboplastin added to plasma
- Tissue Thromboplastin activates the Extrinsic Clotting Pathway which is fast (compared with Intrinsic Clotting Pathway)
III. Precautions
- International Normalized Ratio (INR) and ProTime (PT) were developed only to monitor Warfarin
- All Clotting Factors except Factor 8 and vWF are synthesized in hepatocytes
- In Cirrhosis and hepatic failure, INR is a marker of decreased hepatic synthetic function
- Cirrhosis may be associated with an increased INR/PT, but may also be Hypercoagulable
- Elevated INR in Cirrhosis does not reflect bleeding risk
IV. Labs: Normal
- International Normalized Ratio (INR)
- See Warfarin (includes INR targets per condition)
- See Warfarin Protocol (includes INR initiation protocols and maintenance dosing)
- See Warfarin Protocol for the Perioperative Period (includes bridging, and perioperative INR targets)
- ProTime (replaced by INR)
- Range: 10-12 sec (11-15 sec in some assays)
V. Causes: Increased
- Cirrhosis and other Advanced Liver Disease (e.g. Acute Hepatic Failure)
-
Clotting Factor deficiency
- Factor I Deficiency
- Factor II Deficiency
- Factor V Deficiency
- Factor VII Deficiency
- Factor X Deficiency
- Disseminated Intravascular Coagulation (DIC)
- Vitamin K Deficiency
- Afibrinogenemia
- Dysfibrinogenemia
- Medications
VI. Causes: Decreased
- Vitamin K supplementation
- Thrombophlebitis
- Medications
- Glutethimide
- Estrogens
- Griseofulvin
- Diphenhydramine