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Clin Chim Acta. 2010 Nov 11;411(21-22):1756-60. doi: 10.1016/j.cca.2010.07.023. Epub 2010 Jul 24.

A superior method to report clinically relevant quality information about the point-of-care INR device performance compared with the International Organization for Standardization guidelines.

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Center for Pharmaceutical Outcomes, The Johns Hopkins Medical Institutions, Baltimore, MD 21287, USA.



A revised ISO guideline was recently published that recommended methods to assess the quality of point-of-care INR measures. We assessed the relative performance of the ISO methods and a method that we developed.


We compared the ability of the ISO and the Shermock methods to predict when the INR measures lead to identical or different clinical decisions. Clinical decisions that were directly measured in a previous trial were used as a standard.


The Shermock method was significantly better (82% of predictions correct) than the revised ISO method (61% correct, p<0.0001) at predicting when two INR measures lead to identical or different clinical decisions. Only 41% of decisions predicted to disagree by the revised ISO method actually disagreed; while only 51% of decisions that actually agreed were correctly predicted.


The Shermock method is superior in providing information that clinicians and patients care most about regarding the quality of the INR measures used to guide clinical decisions. Regulatory agencies should strongly consider incorporating the Shermock method into the device approval process. Local clinical laboratories should consider using the Shermock method in quality assurance assessments.

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