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International Normalized Ratio determination using calibrated reference plasmas

A R Hubbard1, S M Margetts, T W Barrowcliffe

  • 1Division of Haematology, National Institute for Biological Standards and Control, South Mimms, Potters Bar, Herts.

British Journal of Haematology
|July 1, 1997
PubMed
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A new method for determining the International Normalized Ratio (INR) using extrapolation reduces variability between laboratories. This approach offers a more consistent and reliable way to measure blood clotting times, improving diagnostic accuracy.

Area of Science:

  • Clinical Chemistry
  • Hematology
  • Laboratory Medicine

Background:

  • The International Normalized Ratio (INR) is crucial for monitoring oral anticoagulant therapy.
  • Conventional INR determination relies on mean normal prothrombin time (MNPT) and local system International Sensitivity Index (ISI), introducing variability.
  • There is a need for more standardized and less variable methods for INR determination.

Purpose of the Study:

  • To compare the conventional INR determination method with an alternative extrapolation method.
  • To assess the inter-laboratory variability of both methods.
  • To evaluate the feasibility of using extrapolation for INR determination without MNPT or ISI.

Main Methods:

  • Developed an alternative INR determination method using extrapolation from a calibration curve with freeze-dried reference plasmas.

Related Experiment Videos

  • Constructed calibration curves by plotting local prothrombin time (PT) against assigned INR values.
  • Six laboratories performed INR determinations on freeze-dried test plasma and frozen patient plasma samples using both conventional and extrapolation methods.

    • Main Results:

    • The extrapolation method yielded an overall mean INR of 2.70 with significantly reduced inter-laboratory variability (3.44% and 4.92%).
    • Conventional methods for the test plasma showed a mean INR of 2.73 with higher inter-laboratory variability (8.92%).
    • Results from freeze-dried test plasma and frozen patient samples showed encouraging similarities, suggesting potential for fresh plasma samples.

    Conclusions:

    • INR determination by extrapolation significantly reduces inter-laboratory variability compared to the conventional method.
    • The extrapolation method offers a more standardized approach to INR measurement, potentially improving clinical consistency.
    • This alternative method eliminates the need for MNPT and local ISI determination, simplifying the process.