Sample carryover in PT-INR determination Is it an issue in Oral Anticoagulant Therapy control?

The quality of Oral Anticoagulant Therapy (OAT) management relies both on the adequacy (safety and effectiveness) of treatment and on the accuracy (precision and trueness) of PT-INR (Prothombin Time - International Normalized Ratio) determination. Since its introduction by Quick in 1935 [1], many efforts have been made to standardise the PT-INR method and to control the several preanalytical, analytical and post-analytical variables that may affect the assay results [2,3]. The introduction of automated techniques has greatly improved the throughput as well as the analytical performance of the assay. However, in some analysers, the robotic pipetting by means of a single sample probe, which comes into contact successively with different specimens, may lead to sample-to-sample carryover, which occurs when a portion of one specimen is transferred into the following one [4,5]. Sample carryover may impair the accuracy of the assay. Following the serendipitous observation of a sample carryover case while performing PT-INR determination, we decided to evaluate the impact of this phenomenon on plasmas from patients undergoing OAT control.