HCUP Methods Series - Agency for Healthcare Research and Quality

All codes in the diagnosis section of ICD-9-CM are classified. In previous versions of thesystem, E codes (External Causes of Injury and Poisoning) were not classified becausethey are used sporadically in inpatient data; hence they were lumped into a singlecategory (CCS 260). Beginning with the 1999 version of the CCS, a classificationsystem for E codes was incorporated. The E code classification was developed by staffat the Centers for Disease and Control and Prevention (Centers for Disease Control,1997). Examples of single-level CCS diagnosis categories are shown in Box 1.Box 1—Examples of single-level CCS diagnosis categoriesDescriptionICD-9-CM 1 diagnosis CCS categorycodes used to mapEssential Hypertension 4011 4019 98Hypertension withcomplications and secondaryhypertension4010 40200 40201 40210 4021140290 40291 4030 40300 403014031 40310 40311 4039 4039040391 4040 40400 40401 4040240403 4041 40410 40411 4041240413 4049 40490 40491 4049240493 40501 40509 40511 4051940591 40599 437299ICD-9-CM codes for the single-level diagnosis CCS categories are presented inAppendix A. The ICD-9-CM code assignments to each category are viewable in theaccompanying executable file that provides the crosswalk from ICD-9-CM diagnosiscodes to single-level CCS categories.Labels for the single-level CCS diagnoses are available in Appendix A1.Procedure CodesThe single-level procedure classification scheme contains 231 mutually exclusivecategories. Many of the categories represent single procedures; however, someprocedures that occur infrequently are grouped according to the body system on whichthey are performed, whether they are used for diagnostic or therapeutic purposes, andwhether they are considered operating room or non-operating room proceduresaccording to diagnosis related groups definitions (DRGs: Diagnosis related groupsdefinitions manual, 1994). Examples of single-level CCS procedure categories areshown in Box 2.1 Additional information about the application of ICD-9-CM diagnosis and procedure codes can be foundlater in this document.HCUP CCS 6/16/2004 5