Research in the Danish health service system: completeness and validity of prescription data, illustrated by analysis of utilization of oral anticoagulants.

We studied the utilization of oral anticoagulants and the degree of completeness and validity of some key research variables from the Danish health service in the county of North Jutland (482 000 inhabitants), studying the records of 12 855 prescriptions of oral anticoagulants during 1991 and 1992. The utilization of oral anticoagulants showed an increase of 16% from 1991 to 1992, when 0.3% of all women and 0.4% of all men were treated during one year. The increase was less than expected based on newly introduced indications for treatment of atrial fibrillation. The following variables were studied: the name (ATC commodity number) and amount of the prescribed drug, the defined daily dose, the personal registration number of the patient, type of prescription (e.g. in writing or by telephone), number of repeat prescriptions, date of prescription issued by the doctor, the registration number of the GP or hospital department (if the prescription is made by a hospital doctor) and date of expedition from the pharmacy. The number of wrong and missing data was less than 1%. The study suggests that Danish prescription information is of such quality that it can be used for pharmacoepidemiological studies.