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Related Experiment Videos

Reliance on prothrombin time ratios causes significant errors in anticoagulation therapy.

H I Bussey1, R W Force, T M Bianco

  • 1Department of Pharmacology, University of Texas Health Science Center, San Antonio 78284-7765.

Archives of Internal Medicine
|February 1, 1992
PubMed
Summary

Warfarin anticoagulation is often inappropriate in the US due to inconsistent use of the international normalized ratio (INR) and variable thromboplastin sensitivity (ISI). Most labs do not report INR, and thromboplastin ISI values are frequently outside the recommended range.

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Area of Science:

  • Clinical Chemistry
  • Pharmacology
  • Hematology

Background:

  • Warfarin anticoagulation management in the US may be suboptimal.
  • Inappropriate intensity can result from not using the international normalized ratio (INR) or thromboplastin international sensitivity index (ISI) outside the 2.2–2.6 range.

Purpose of the Study:

  • To assess the reporting of INR values and the range of thromboplastin ISI used in US hospital laboratories.
  • To determine the extent of variability in thromboplastin sensitivity and its impact on warfarin therapy.

Main Methods:

  • Surveyed 53 hospital laboratories regarding thromboplastin sensitivity and INR reporting.
  • Collected additional thromboplastin sensitivity data from 140 Stroke Prevention in Atrial Fibrillation study participants.
  • Confirmed thromboplastin sensitivity ranges with three major manufacturers.

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Main Results:

  • Only 21% of surveyed labs reported INR results; 30% could not provide ISI data.
  • 20%–24% of labs used unlabeled thromboplastin; 8%–20% used thromboplastins with the recommended ISI (2.2–2.6).
  • Manufacturers offered thromboplastins with ISI from 1.2 to 2.8, but none were within the 2.2–2.6 range at the time.

Conclusions:

  • Most US laboratories do not report INRs, leading to inappropriate warfarin therapy.
  • Variability in thromboplastin sensitivity yields misleading prothrombin time ratio results.
  • Research relying on INR or ISI data may need reevaluation due to data inconsistencies.