Background: To use the standard DRG grouper, software records must be presented using the diagnostic and procedure codes in the International Classification of Diseases--9th revision--Clinical Modification (ICD9 CM). In Italy, diagnoses are coded in the International Classification of Disease--9th revision (ICD9) and it was necessary to perform an ICD9-ICD9 CM diagnostic coding translation.
Aim of the study: To measure the number of misallocations (in the assignation of DRGs) due to the utilization of ICD9 rather than ICD9 CM.
Methods: Discharge data on 125 admissions (95% confidence interval for the 4% error rate in the estimate of percentage of misallocations) in 1996 to the cardiology division of Castelfranco Veneto, were assigned to HFCA-DRG, 10th version. A pair of DRGs was assigned for every admission: one DRG was assigned coding directly in ICD9 CM and the other one was coded in ICD9 and then transcoded in ICD9 CM through the Italian coding translation. Lastly, each pair of DRGs was compared by matching.
Results: There were 7 misallocations (5.6%): 4 misallocations (3.2%) were observed in the description of recent AMI (less than 8 weeks old); 2 misallocations (1.6%) were due to the different coding of postmyocardial infarction syndrome; 1 misallocation (0.8%) was observed in shock DRG.
Conclusions: In cardiology, the percentage of misallocation is higher than in other divisions that, in other papers, showed a percentage of misallocation that did not exceed 2.0%. In particular, by using ICD9 rather than ICD9 CM, DRGs of AMI are over-estimated and DRG of coronography are under-estimated. This word showed that in Italy, above all for the cardiology divisions, it would be important to introduce the ICD9 CM in order to have a more specific disease classification and to have DRGs that are standardized with the international ones.