There are considerable drawbacks to oral anticoagulant for monitoring patients at home which should lead family physicians to discuss alternative or enhanced solutions: a cross-sectional study

Background: INR (International Normalized Ratio) is the biological reference test for the monitoring of vitamin K antagonist (VKA) therapy. Overdosage of VKAs causes about 17,000 hospitalizations and 5,000 deaths each year in France. To avoid these complications, monitoring and blood sampling conditions must be rigorous. In France, more than half of INRs are carried out at home. The aim was to determine blood-sampling conditions at home, transit time and the quality of the laboratory reagents used. Method: Questionnaire-based, descriptive epidemiological cross-sectional prevalence study involving home care nurses, family physicians (FPs) and clinical laboratories. Setting: Brittany, France, 2008. Study of the pre-analytical phase of INRs sampled at home and its influence on INR results. Results: The study included 291 FPs, 249 home care nurses, and 49 laboratories. 32.5% of reported INRs were outside the therapeutic range. Samples were drawn into unsuitable tubes in 5.5% of cases and delivered in a chilled condition in 9% of cases. In urban areas 50% of the tubes took more than 2 hours to reach the laboratory compared with 71% from rural areas. The average International Sensitivity Index (ISI) of the thromboplastin was 1.62. The INRs provided by the laboratories were not analyzable in 64.7% of cases where blood samples had been taken at home. Conclusion: Blood sample quality, transit time and the reagents used are currently inadequate. The majority of INRs taken at home are not reliable. FPs should consider these drawbacks in comparison with alternative solutions to increase patient safety.