Results of the performance verification of the CoaguChek XS system

This is the first paper reporting a performance verification study of a point-of-care (POC) monitor for prothrombin time (PT) testing according to the requirements given in chapter 8 of the International Organization for Standardization (ISO) 17593:2007 standard "Clinical laboratory testing and in vitro medical devices - Requirements for in vitro monitoring systems for self-testing of oral anticoagulant therapy". The monitor under investigation was the new CoaguChek XS system which is designed for use in patient self testing. Its detection principle is based on the amperometric measurement of the thrombin activity generated by starting the coagulation cascade using a recombinant human thromboplastin.

The system performance verification study was performed at four study centers using venous and capillary blood samples on two test strip lots. Laboratory testing was performed from corresponding frozen plasma samples with six commercial thromboplastins. Samples from 73 normal donors and 297 patients on oral anticoagulation therapy were collected. Results were assessed using a refined data set of 260 subjects according to the ISO 17593:2007 standard.

Each of the two test strip lots met the acceptance criteria of ISO 17593:2007 versus all thromboplastins (bias -0.19 to 0.18 INR; >97% of data within accuracy limits). The coefficient of variation for imprecision of the PT determinations in INR ranged from 2.0% to 3.2% in venous, and from 2.9% to 4.0% in capillary blood testing. Capillary versus venous INR data showed agreement of results with regression lines equal to the line of identity.

The new system demonstrated a high level of trueness and accuracy, and low imprecision in INR testing. It can be concluded that the CoaguChek XS system complies with the requirements in chapter 8 of the ISO standard 17593:2007.