Linking a hospital diabetes database and the National Health Service Central Register: a way to establish accurate mortality and movement data

We have established a records linkage between 'Diabeta' (the computerized clinical records system in the Diabetes Unit of St Thomas' Hospital) and the National Health Services Central Register (NHSCR) of the United Kingdom. Over 7000 diabetic patient records have been collected since 1973. Demographic data on all diabetic patients were retrieved and submitted to the NHSCR via a floppy disk. A matching system (automatic or manual) was used by the NHSCR to identify deceased patients and the most recent demographic data was provided on patients alive. This linkage resulted in an update of 91% of records in Diabeta. The findings of the update included: (1) 86% of diabetic patient's death had not been notified to the hospital and were not recorded on Diabeta. Mortality can now be assessed accurately as an outcome measure in our diabetic population. (2) Provision of the NHS number to Diabeta, as before it was not available on many patients seen in the hospital. The NHS number is a key patient identifier which can be used to exchange information within the NHS-wide network. (3) Diabetes was recorded as a cause of death in only 36% of death certificates. Analyses of death certificates alone must thus give poor information about mortality in diabetes. (4) Geographical location of patients on the database was updated, enabling tracing of patients for long-term studies and analyses of movement.