Background: The International Classification for Primary Care (ICPC) has been the standard classification for diagnoses on sickness certificates and bills for services to the National Insurance Administration in Norway since 1992. Coding according to ICPC is compulsory for all general practitioners.
Objective: The objective of the present study was to describe the introduction of ICPC in Norway, to comment on introduction problems, and to examine the compliance and validity of coding.
Methods: The study was based on statistics for episodes of sickness certification in the National Benefit Absence Register.
Results: In 1994, the underlying medical diagnosis was coded in 98% of the sickness absence episodes lasting more than 2 weeks. Component 1 codes (symptom codes) were used in 23% of episodes, compared with 26-31% in practice studies.
Conclusions: ICPC-coded data in a large Norwegian register appear promising. Most doctors do accurate and careful work in coding, and data appear to be of acceptable quality for further analysis. It is a matter of concern, however, that as many as 23% of episodes had component 1 codes, since these certificates were issued during follow-up encounters. The introduction of ICPC coding has enabled researchers to use diagnoses in the analyses of sickness absence. The growing use of ICPC in general practice has made multi-practice studies possible. The introduction of criteria is mandatory for the improvement of validity in diagnostic coding.