Characteristics of Anticoagulant Therapy and Comorbidity Related to Overanticoagulation

TLDR

Hemorrhage risk rises sharply with coumarin anticoagulants when INR reaches ≥6.0. The study aimed to estimate overanticoagulation incidence and its association with anticoagulant therapy characteristics and comorbidities. A prospective cohort of 17,056 anticoagulation clinic outpatients with a nested case‑control analysis compared 300 INR≥6.0 cases to 302 matched controls. Incidence of INR≥6.0 was 7.8 per 10,000 treatment days in prevalent users and 22.5 per 10,000 days in incident users, acenocoumarol increased risk versus phenprocoumon, and impaired liver function, congestive heart failure, diarrhea, and fever were risk factors, indicating that intensified monitoring or avoidance could reduce bleeding complications.

Abstract

Summary The risk of hemorrhage when using coumarin anticoagulants sharply increases when the International Normalised Ratio (INR) is ≥6.0. We performed a prospective cohort study with a nested case-control design among 17,056 outpatients of an anticoagulation clinic to determine the incidence of overanticoagulation and to study the association between overanticoagulation and characteristics of anticoagulant therapy and comorbidity. The incidence rate of an INR ≥6.0 was 7.8 per 10,000 treatment days in prevalent users on the starting date and 22.5 per 10,000 treatment days in incident users during the study period. 300 cases with an INR ≥6.0 were compared with 302 randomly selected matched controls with an INR within the target zone. Patients on acenocoumarol had an increased risk of an INR ≥6.0 compared to patients on phenprocoumon. Regarding comorbidity, impaired liver function, congestive heart failure, diarrhea and fever were risk factors for overanticoagulation. Increased monitoring of INR values if risk factors are present or avoidance of risk factors could prevent excess anticoagulation and potential bleeding complications.