Primary health care ICD--a tool for general practice research.

The International Classification of Diseases (ICD) has become the only diagnostic classification system of international standard that allows reliable comparisons of epidemiological data between countries, parts of a country, levels of health care systems, or different periods of time. However, for primary health care purposes it is too specific to describe problems relevant to the work of general practitioners (GPs). Tools are thus needed to 'compress' data in primary health care for educational, administrative and research purposes. The objective of this paper was to introduce a diagnosis coding system that can be used in primary health care settings for these purposes. Principal diagnoses, as assessed by medical doctors, were collected from 20,648 patient visits. After primary coding, according to the ICD on a five-digit scale, the diagnoses were grouped into larger entities, which reduced the number of diagnoses to one eighth of the original number. The ten most common original five-digit diagnoses accounted for one quarter of all consultations, whereas the ten most common diagnoses counted for one half of all consultations after compressing the data into new categories. Analysing epidemiological data in the records of primary health care by the ICD offers benefits because of the latter's wide use. These are discussed below.