Aims Ð To determine the sensitivity and speci®city of each ICD9 code for a diagnosis of de®nite or possible myocardial infarction (MI) from the perspective of the Myocardial Infarction Causality Study (MICA) and to use these data to estimate the likely number of MICA cases in Scotland that would be undetected were these codes omitted from the study.
Setting Ð Women resident and registered with general practitioners in the Tayside region of Scotland between October 1993 and October 1995.
Method Ð All SMR1 records of Tayside hospitalizations containing ICD9 (International Classi®cation of Diseases, ninth revision) codes for myocardial infarction (410) or possible myocardial infarction (411, 412, 413, 414, 427.4, 427.5, 786.5) were identi®ed for women aged between 16 and 44 years between 1 October 1993 and 15 October 1995. Original case records were sought and each episode abstracted using a prede®ned form. Records were independently scrutinized by two consultant cardiologists blinded to the SMR1 code. Cases were categorized as de®nite MI, possible MI or unlikely MI. Where there was disagreement between the two cardiologists, the pro®les for such events were examined by a third cardiologist who acted as the ®nal adjudicator. The adjudicator's verdict was, in this study, considered dominant. The sensitivity, speci®city and positive predictive value of each ICD9 code was determined.
Results Ð Two hundred and ®fty-three women ful®lled the SMR1 search criteria. Case records of 204 (81%) were retrieved but four case records contained no data on the admission of interest and were classi®ed as invalid. Forty-six of the 200 remaining patients were ineligible for the MICA study leaving 154 records for evaluation. There were 12 patients who had a discharge code for MI (ICD9 410). Of these, 11 were judged as a de®nite MI by both cardiologists. One event (discharge code ICD9 410) was judged as possible' by one cardiologist and unlikely' by the other. The adjudicator subsequently judged this event as de®nite'. Another six events were subsequently judged as possible'. Thus, after adjudication, 12 cases of de®nite MI and six cases of `possible' MI were identi®ed. The sensitivity and speci®city of ICD9 code 410 was 67% and 100% respectively. The positive predictive value was 100%. The sensitivity of code 411 was 5.6%. The speci®city was 99% and the positive predictive value was 50%. Code 413 had a sensitivity of 5.6% with a speci®city of 94% and a positive predictive value of 9.1%. Code 414 also had a sensitivity of 5.6%. The speci®city was 86% and the positive predictive value was 4.5%. Code 786.5 had a sensitivity of 17%, a speci®city of 23% and a positive predictive value of 2.5%. Code 427.5 failed to identify any de®nite or possible cases.
Conclusions Ð In the MICA Study, ICD9 code 410 was found to be the most robust. All 12 patients judged to have had a de®nite MI had the appropriate discharge code (ICD9 410). The six patients judged CCC 1053±8569/98/050311±08$17.50