Identifying patients with ischaemic heart disease in general practice: cross sectional study of paper and computerised medical records.

OBJECTIVES: To identify patients with ischaemic heart disease by using a practice computer and to estimate the work required to do so.
DESIGN: Cross sectional study. Data from the notes and from the computer records of 1680 patients were used to build a database. This was used to compare different methods of identifying patients with ischaemic heart disease.
SETTING: 11 general practices in the Battersea primary care group in south London.
SUBJECTS: 1 in 40 random sample of patients aged 45 or older. MAIN OUTCOME MEASURES: Numbers of patients identified with ischaemic heart disease.
RESULTS: The combination of the Read code for ischaemic heart disease (G3) and a prescription for a nitrate had a 73% sensitivity and a yield (100/positive predictive value) of one case of ischaemic heart disease for every 1.2 sets of notes reviewed. By searching the records of patients also receiving aspirin, atenolol, digoxin, or a statin, the sensitivity was increased to 96% but the yield fell to one in three.
CONCLUSION: Although commonly used to identify cases, a computer search for G3 code or nitrate missed almost 30% of patients with ischaemic heart disease. A substantially higher percentage of patients can be identified by adding other drugs to the search strategy.