A STUDY TO DETERMINE THE SENSITIVITY AND SPECIFICITY OF HOSPITAL DISCHARGE DIAGNOSIS DATA USED IN THE MICA STUDY

Aims - To determine the sensitivity and specificity of each ICD9 code for a diagnosis of definite or possible myocardial infarction (MI) fro m the perspective of the Myocardial Infarction Causality Study (MICA) and to use these data to estimate the likely number of MICA cases in S cotland that would be undetected were these codes omitted from the stu dy. Setting - Women resident and registered with general practitioners in the Tayside region of Scotland between October 1993 and October 19 95. Method - All SMR1 records of Tayside hospitalizations containing I CD9 (International Classification of Diseases, ninth revision) codes f or myocardial infarction (410) or possible myocardial infarction (411, 412, 413, 414, 427.4, 427.5, 786.5) were identified for women aged be tween 16 and 44 years between 1 October 1993 and 15 October 1995. Orig inal case records were sought and each episode abstracted using a pred efined form. Records were independently scrutinized by two consultant cardiologists blinded to the SMR1 code. Cases were categorized as defi nite MI, possible MI or unlikely MI. Where there was disagreement betw een the two cardiologists, the profiles for such events were examined by a third cardiologist who acted as the final adjudicator. The adjudi cator's verdict was, in this study, considered dominant. The sensitivi ty, specificity and positive predictive value of each ICD9 code was de termined. Results - Two hundred and fifty-three women fulfilled the SM R1 search criteria. Case records of 204 (81%) were retrieved but four case records contained no data on the admission of interest and were c lassified as invalid. Forty-six of the 200 remaining patients were ine ligible for the MICA study leaving 154 records for evaluation. There w ere 12 patients who had a discharge code for MI (ICD9 410). Of these, 1 1 were judged as a definite MI by both cardiologists. One event (dis charge code ICD9 410) was judged as 'possible' by one cardiologist and 'unlikely' by the other. The adjudicator subsequently judged this eve nt as 'definite'. Another six events were subsequently judged as 'poss ible'. Thus, after adjudication, 12 cases of definite MI and six cases of 'possible' MI were identified. The sensitivity and specificity of ICD9 code 410 was 67% and 100% respectively. The positive predictive v alue was 100%. The sensitivity of code 411 was 5.6%. The specificity w as 99% and the positive predictive value was 50%. Code 413 had a sensi tivity of 5.6% with a specificity of 94% and a positive predictive val ue of 9.1%. Code 414 also had a sensitivity of 5.6%. The specificity w as 86% and the positive predictive value was 4.5%. Code 786.5 had a se nsitivity of 17%, a specificity of 23% and a positive predictive value of 2.5%. Code 427.5 failed to identify any definite or possible cases . Conclusions - In the MICA Study, ICD9 code 410 was found to be the m ost robust. All 12 patients judged to have had a definite MI had the a ppropriate discharge code (ICD9 410). The six patients judged to have had a possible MI all had discharge codes other than that for MI (410) . However, identifying these six patients required the validation of a further 160 events - giving a combined sensitivity of 33%, a specific ity of 0% and a positive predictive value of only 3.8%. The use of ICD 9 codes 411, 413, 414, 427.5 and 786.5 must, therefore, only be employ ed when circumstances fully justify the additional workload. (C) 1998 John Wiley & Sons, Ltd.