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Why is the standardization of prothrombin time a problem?

I Talstad1

  • 1Fürst Medisinsk Laboratorium, Oslo, Norway.

Haemostasis
|March 17, 2001
PubMed
Summary

Prothrombin time (PT) standardization remains challenging. Correcting for the protein induced by vitamin K absence (Pivka) inhibitor offers a promising path for improved PT assay standardization.

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Area of Science:

  • Clinical Chemistry
  • Hematology
  • Medical Diagnostics

Background:

  • Prothrombin time (PT) standardization has been a persistent issue for over 50 years.
  • Previous standardization methods, including Quick's PT assay and WHO ratio methods (1977, 1983), have proven unsatisfactory due to neglected intercepts and erroneous calibration materials.
  • The international normalized ratio (INR) system, based on a simplified method, has not achieved superior standardization compared to uncorrected ratios.

Purpose of the Study:

  • To analyze the reasons behind the long-standing difficulties in prothrombin time (PT) standardization.
  • To evaluate the effectiveness of various PT standardization methods, including ratio methods and the international normalized ratio (INR).
  • To identify a preferable method for achieving accurate PT standardization.

Main Methods:

  • Analysis of historical and current PT standardization methodologies, including Quick's PT assay, WHO ratio methods, and the international sensitivity index.
  • Evaluation of the impact of calibration materials and conversion complexities on standardization.
  • Assessment of uncorrected and protein induced by vitamin K absence (Pivka)-corrected coagulation activities.

Main Results:

  • Initial PT standardization attempts and WHO-accepted ratio methods failed to achieve consistent standardization.
  • The international sensitivity index did not improve standardization of international normalized ratios (INR) over uncorrected ratios.
  • Uncorrected coagulation activities exhibited poor standardization due to assay sensitivity variations for Pivka inhibitors, with therapeutic ranges covering only 70% (INR) and 10-20% (coagulation activities) of their scales.

Conclusions:

  • Standardization of prothrombin time (PT) assays has been problematic due to inherent limitations in existing methods.
  • Protein induced by vitamin K absence (Pivka)-corrected coagulation activities, when standardized against an international reference assay, may represent a more reliable approach.
  • Further research into Pivka-corrected methods is recommended for improved PT assay standardization and clinical utility.

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