Warfarin anticoagulation: difficulties in interpretation of the prothrombin time

Area of Science:

• Clinical Chemistry
• Hematology
• Pharmacology

Background:

• Prothrombin time (PT) is a critical measure for monitoring warfarin therapy.
• Accurate PT measurements are essential for safe and effective anticoagulation.
• In vitro factors can influence coagulation test results, potentially impacting clinical decisions.

Purpose of the Study:

• To investigate the effect of blood collection tube material on prothrombin time measurements.
• To determine if collection tube type influences PT in patients receiving warfarin or coumadin therapy.
• To assess the clinical implications of altered PT results due to collection tube variations.

Main Methods:

• Prothrombin time was measured in normal individuals and patients on warfarin therapy.
• Blood samples were collected using various types of blood collection tubes.
• The influence of time and temperature on PT shortening was evaluated for coumadin-treated patients.

Main Results:

• A significant shortening of prothrombin time was observed when blood was collected in non-polypropylene tubes.
• This effect was noted in both normal subjects and patients undergoing warfarin therapy.
• The in vitro shortening of PT was dependent on both collection time and temperature.

Conclusions:

• The material of the blood collection tube is a critical pre-analytical variable affecting PT results.
• Using non-polypropylene collection tubes can lead to falsely low PT values in patients on warfarin.
• These findings highlight the potential for serious clinical errors in warfarin derivative dosage due to improper blood collection.