The impact of different coding systems on DRG assignment and data

The Diagnosis Related Group (DRG) classification system is widely used to describe the casemix of acute care hospitals, making it possible to compare the casemix of hospitals from different countries. However, in order to fully understand these comparisons, it is necessary to clarify the impact which the different coding systems used in various countries may have had on the results. The DRG system is based on codes from the International Classification of Diseases 9th Revision Clinical Modification (ICD9CM). Countries which use other coding systems convert, i.e. map, their codes into the nearest ICD9CM equivalent before allocating the DRGs. The impact of mapping on both medical and surgical DRGs is discussed and new titles are given for the affected DRGs. As far as possible, problems caused by mapping are distinguished from those caused by differences in coding practices. Based on the analysis of the classification systems, the mapping tables and the resulting DRG data, it is concluded that using mapped data does not have a great impact on the DRGs. Only 37 DRGs (7.8%), 15 medical and 22 surgical classes, are affected by mapping problems. However, while the scale of these problems is not large, given the large number of different surgical classification systems currently in use in Europe, the introduction of a standard surgical classification system for Europe is recommended.