Diagnosing and Diagnosis Coding of Dementias in Claims Data from German Statutory Health Insurance

Objective: On the basis of data from one German Sickness Fund we analyzed which medical discipline coded the incident diagnosis of dementia in ambulatory medical care in Germany, which type of dementia was coded and how the initial code eventually changed during the year of incidence. Methods: Claims data of 1,848 insured people aged >= 65 years in 2004 with incident dementia were analyzed by means of descriptive statistics. Results: The diagnosis within the first quarter of the incidence year was coded by the GP in 71%, by a psychiatrist or neurologist in 14%, by both in 6% and by other disciplines in 9% of the cases. The percentage of unspecified diagnoses was 62% among GPs and 46% among psychiatrists or neurologists, a number differing largely from epidemiological studies. In 27% of the cases patients received two or more different dementia diagnoses during the incidence year. Conclusion: Studies and care concepts regarding dementia on the basis of diagnosis codes in ambulatory claims data should be interpreted with great caution.