The Clinical Classifications Software Refined (CCSR) for ICD-10-CM diagnoses aggregates over 70,000 ICD-10-CM diagnosis codes into a manageable number of clinically meaningful categories.

About 80 percent of ICD-10-CM diagnosis codes are classified by only one CCSR category. For the ICD-10-CM diagnosis codes where there may be more than one CCSR category mapped for a given code, AHRQ has created a supplemental default categorization scheme for the CCSR that can be used in analyses of principal (or first-listed) diagnosis. Under this default categorization scheme, each ICD-10-CM diagnosis code is assigned to a mutually exclusive category. In general, the default assignment is based on clinical coding guidelines, clinical input on the etiology and pathology of diseases, coding input on the use of and ordering of ICD-10-CM codes on a billing record, and standards set by other Federal agencies. The guidelines for determining the default CCSR are ordered in a hierarchical fashion. If a code does not fit the first rationale, then the next rationale is considered, and so forth until an appropriate rationale is determined. The default categorizations chosen by AHRQ will not apply to all situations. Users may choose to assign different default CCSR categories for ICD-10-CM codes that are cross-classified, based on their own reporting purpose, research design, study purpose, or clinical preferences. Please see Appendix B of the User Guide for the CCSR for ICD-10-CM Diagnoses for more information.

Inpatient Data

There are ICD-10-CM diagnosis codes that are not to be reported as a principal diagnosis in inpatient data (according to Medicare Code Edits). These codes do not have a default categorization assigned. Their default categorization is indicated by the CCSR category XXX000 with the rationale of "Invalid principal diagnosis". Examples of codes included in this group are external causes of morbidity codes (i.e., codes beginning with V00-Y99), underdosing codes (i.e., codes beginning with T36-T50 with fifth or sixth character "6"), and adverse effect codes (i.e., codes beginning with T36-T50 with fifth or sixth character "5").

Outpatient Data

The assignment of the default CCSR is based on inpatient coding guidelines that assume there has been sufficient time and testing to determine a definitive diagnosis. This is not always true in an outpatient setting such as the emergency room. There are also ICD-10-CM diagnosis codes that are not to be reported as a first-listed diagnosis in outpatient data (according to ICD-10-CM coding guidelines). Their default categorization is indicated by the CCSR category XXX111 with the rationale "Invalid first-listed diagnosis". Examples of codes included in this group are external causes of morbidity codes, underdosing codes, and diagnoses for anemia or genetic susceptibility to neoplasms (e.g., code D630 for anemia in neoplastic diseases and codes starting with Z15 for genetic susceptibility for malignant neoplasms). Please see Appendix C of the User Guide for the CCSR for ICD-10-CM Diagnoses for more information.

DXCCSR_DEFAULT_DX1 is coded as follows:

• aaannn if the principal (or first-listed) diagnosis code (I10_DX1) is valid by the HCUP criteria (HCUP edit check EDX02), which allows a year window (six months before and six months after) around the official ICD-10-CM coding changes (usually October 1), for anticipation of or lags in response to official ICD-10-CM coding changes.
• DXCCSR is blank, if there is no principal (or first-listed) diagnosis code (I10_DX1 = " ").
• DXCCSR is set to invalid (InvlDX), if the principal (or first-listed) diagnosis code (I10_DX1) is invalid by the HCUP criteria (EDX02), or inconsistent (.C), if the principal (or first-listed) diagnosis code (I10_DX1) is inconsistent with age (EAGE04 and EAGE05) or sex of the patient (EDX03).

Information on the assignment of ICD-10-CM diagnoses to the CCSR categories and labels for the CCSR categories is available on the HCUP User Support website under Tools and Software (CCSR for ICD-10-CM Diagnoses).