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The individual systematic difference between CoaguChek and STA-SPA

Arne Åsberg1, Hilde Hegseth1, Maria Averina2

  • 1a Department of Clinical Chemistry , Trondheim University Hospital , Trondheim , Norway.

Scandinavian Journal of Clinical and Laboratory Investigation
|February 20, 2019
PubMed

Insights

Patient self-testing using CoaguChek shows variable PT-INR differences compared to hospital labs. A single conversion formula cannot make results directly comparable due to significant between-subject variation.

Area of Science:

  • Clinical Chemistry
  • Medical Devices
  • Pharmacoeconomics

Background:

  • Point-of-care testing (POCT) devices like CoaguChek aim to simplify PT-INR monitoring for patients on anticoagulant therapy.
  • Discrepancies between POCT devices and central laboratory results can impact clinical decision-making.
  • The extent of patient-specific systematic differences in PT-INR measurements between CoaguChek and laboratory methods is not well-quantified.

Purpose of the Study:

  • To quantify the between-subject variation in systematic PT-INR differences between CoaguChek and a hospital laboratory method (STA-SPA+).
  • To determine the proportion of patients exhibiting significant PT-INR measurement differences.
  • To assess the feasibility of a universal conversion formula for CoaguChek results.

Main Methods:

  • Analysis of simultaneously collected PT-INR data from 103 patients using CoaguChek and the STA-SPA+ laboratory method.
  • Exclusion of patients with outlying results.
  • Application of mixed-effects models to estimate individual patient slopes and intercepts, characterizing the systematic relationship between the two methods.
  • Calculation of the fraction of patients with a systematic difference exceeding 0.3 INR units across different PT-INR levels.

Main Results:

  • The mean individual slope was 1.113 (SD 0.137) and the mean intercept was -0.151 (SD 0.208).
  • The proportion of patients with a systematic difference > 0.3 INR units increased from 15% at PT-INR 2.5 to 50% at PT-INR 4.
  • Significant between-subject variability in the systematic difference between CoaguChek and STA-SPA+ was observed.

Conclusions:

  • The systematic PT-INR difference between CoaguChek and the STA-SPA+ method varies considerably among individual patients.
  • A single, common formula is insufficient to ensure direct comparability between CoaguChek and hospital laboratory PT-INR results.
  • Individualized calibration or careful interpretation of CoaguChek results is necessary for accurate anticoagulant management.

Keywords:
Between-subject variationCoaguChekinternational normalized ratiomethod comparisonpoint-of-care testingwarfarin

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