The Australasian Reference Thromboplastin: II. Are corrected prothrombin ratios valid?

Area of Science:

• Clinical Chemistry
• Pharmacology
• Hematology

Background:

• Warfarin therapy requires regular monitoring of prothrombin time (PT) using thromboplastin reagents.
• Different thromboplastins (e.g., Australasian Reference Thromboplastin, Simplastin) can yield varying PT results.
• Accurate PT monitoring is crucial for managing anticoagulation and preventing adverse events.

Purpose of the Study:

• To comparatively analyze the performance of Australasian Reference Thromboplastin and Simplastin in patients on long-term Warfarin therapy.
• To investigate the linearity and comparability of these two thromboplastins across different prothrombin ratio ranges.
• To assess the clinical implications of using linear calibration for corrected ratios, particularly at extreme values.

Main Methods:

• A comparative study involving 373 patient samples from individuals on long-term Warfarin therapy.
• Determination of calibration constants for both thromboplastins for patients within and outside the therapeutic prothrombin ratio range.
• Analysis of the relationship between the two thromboplastins' results, focusing on linearity and potential logarithmic correlations.

Main Results:

• Different calibration constants were observed for patients with prothrombin ratios within and outside the therapeutic range.
• The comparability between Australasian Reference Thromboplastin and Simplastin was found to be linear only within a specific, limited range of prothrombin ratios.
• A curved, potentially logarithmic, relationship was identified at the extreme ends of the prothrombin ratio spectrum.

Conclusions:

• Standard linear calibration may not be universally applicable for comparing thromboplastin results across all prothrombin ratio ranges.
• Caution is advised when interpreting corrected ratios calculated linearly, especially for prothrombin ratios exceeding 4.0, due to potential clinical significance.
• The findings highlight the need for careful selection and validation of thromboplastins in Warfarin monitoring to ensure accurate anticoagulation management.