Establishing an oral anticoagulant monitoring service in a multiethnic developing country.

We describe the establishment of an International Normalized Ratio (INR)-based system for monitoring oral anticoagulant therapy in a multiethnic developing country. There was significant variation in geometric mean normal prothrombin time among ethnic groups: 12.7 s for Indians, 13.4 s for Africans and 13.7 s for subjects of mixed ancestry. About 4129 INR measurements were performed in the first 2 years. The majority (55.2%) of achieved INRs were subtherapeutic. We found 31 (0.8%) instances of severe overanticoagulation (INR > 8.0). There were no bleeding manifestations in 24 (77%) of them. Only two experienced life-threatening haemorrhage. The management of bleeding and excessive anticoagulation was not always in accordance with international recommendations. The high incidence of underanticoagulation in Trinidad and Tobago may be due to genetically determined warfarin resistance or underdosing. Oral anticoagulant monitoring in Trinidad and Tobago could benefit from the centralization of such services to designated clinics with specialized staff and computer-assisted dosing which adopt internationally accepted guidelines for practice.