Classifications in routine use: Lessons from ICD-9 and ICPM in surgical practice

Objective: Classifications of diagnoses and procedures are very important f or the economical as well as the quality assessment of surgical departments . They should reflect the morbidity of the patients treated and the work do ne. The authors investigated the fulfillment of these requirements by ICD-9 (International Classification of Diseases: 9th Revision) and OPS-301, a Ge rman adaptation of the ICPM (International Classification of Procedures in Medicine), in clinical practice. Design: A retrospective study was conducted using the data warehouse of the Surgical Center II at the Medical Faculty in Essen, Germany. The sample in cluded 28,293 operations from the departments of general surgery, neurosurg ery, and trauma surgery. Distribution of cases per ICD-9 and OPS-301 codes, aggregation through the digits of the codes, and concordance between the c lassifications were used as measurements. Median and range were calculated as distribution parameters. The concentration of cases per code was graphed using Lorenz curves. The most frequent codes of diagnoses were compared wi th the most frequent codes of surgical procedures concerning their medical information. Results: The total number of codes used from ICD-9 and OPS-301 went up to 1 4 percent, depending on the surgical field. The median number of cases per code was between 2 and 4. The concentration of codes was enormous: 10 perce nt of the codes were used for about 70 percent of the surgical procedures. The distribution after an aggregation by digit was better with OPS-301 than with ICD-9. The views with OPS-301 and ICD-9 were quite different. Conclusion: Statistics based on ICD-9 or OPS-301 will not properly reflect the morbidity in different surgical departments. Neither classification ade quately represents the work done by surgical staff. This is because of an u neven granularity in the classifications. The results demand a replacement of the ICD-9 by an improved terminological system in surgery. The OPS-301 s hould be maintained and can be used at least in the medium term.