Plots of interlaboratory international normalized ratio (INR) coefficients of variation (CVs) vs median Royal College of Pathologists of Australasia Quality Assurance Program (RCPAQAP) INR values. Data shown separately for years 2017 to 2019 Stago and 2021 to 2023 Werfen, and for all mechanical clot detection instruments (including Stago analyzers), all optical clot detection instruments (including Werfen analyzers), all methods, New South Wales (NSW) Health Pathology network laboratories (n = 27 for 35 instruments). Resulting linear regression lines for each data set also shown. There is near-horizontal linearity for NSW Health Pathology network laboratories, with CVs in general less than 5%, suggesting little variation in CVs according to INR value. In contrast, upward trajectories are generally evident for all methods or for all mechanical or optical test systems (ie, CVs range upward with increasing INR). The range of CVs was as follows: (1) all mechanical clot detection instruments years 2017-2019: 5.6% to 12.6% and for years 2020-2023: 5.6% to 14.7%; (2) all optical clot detection instruments years 2017-2019: 5.1% to 12.2% and for years 2020-2023: 2.0% to 13.7%; (3) all methods years 2017-2019: 5.1% to 12.2% and for years 2020-2023: 2.0% to 13.7%; (4) NSW Health Pathology Network (Pathology West, West, or Rural/Regional) laboratories years 2017-2019 (mechanical): 3.2% to 7.4% and for years 2020-2023 (optical): 0% to 5.9%. The 0% CV (arrow) was achieved on a sample reported by the network as yielding an INR of 1.0 by all laboratories/instruments submitting INR data.