Setting for current study. The Institute of Clinical Pathology and Medical Research (ICPMR) laboratory, based at Westmead Hospital, was established in 1975 as a stand-alone laboratory to service the hemostasis pathology needs of Westmead Hospital. The ICPMR laboratory became part of New South Wales (NSW) Health Pathology when it was founded in 2012 and later became part of the Pathology West network of laboratories (n = 27) (still part of NSW Health Pathology). Subsequently, the Pathology West network was split into 2 functional units (named West and Rural/Regional) but together still comprised the same 27 laboratories of the former Pathology West. We report on interlaboratory variability in international normalized ratio (INR) testing across all 27 laboratories (35 instruments) during 3 years while using mechanical clot detection analyzers and reagents from Stago (2017-2019) compared to 3 years while using optical clot detection analyzers and reagents from Werfen (2021-2023) (see also TABLE 1).