OBJECTIVES:

Coding algorithms are critical for identifying patient samples, comorbidities, and outcomes in studies of claims or electronic medical record data, but algorithms developed with International Classification of Diseases, Ninth Revision (ICD-9) codes are obsolete in current data. The present study sought to compare ICD-9 to ICD-10 crosswalks from General Equivalence Mappings (GEMs) and compare them to crosswalks derived by a clinician and clinical coder, to evaluate whether automated methods are sufficient for deriving ICD-10 algorithms.

METHODS:

Ten conditions from various therapeutic areas were selected for comparison. Existing ICD-9 algorithms were entered into GEMs to derive ICD-10 crosswalks, and a physician and clinical coder completed a questionnaire to guide the development of ICD-9 to ICD-10 crosswalks for the same conditions. Differences between the crosswalks were summarized using descriptive statistics and the theoretical impact of the differences were assessed qualitatively.

RESULTS:

Crosswalks identified by the physician/coder were typically far more inclusive than those from GEMs. Crosswalks from GEMs were missing a mean of 147.7 codes (median: 45; range: 19–462) compared to those from the physician/coder, while the physician/coder crosswalks missed far fewer (mean: 11.3; median: 5.5; range: 0–53) compared to GEMs. Crosswalks for diabetes, diabetic neuropathy, hypoglycemia, and peripheral vascular disease had the most discrepancies (>130) while crosswalks for acute myocardial infarction and hypertension had the fewest (<25). Generally, conditions with the most discrepancies included those with various etiologies, conditions with a variable clinical definition, those that may be a side effect of medications, and those that require procedure codes to supplement identification.

CONCLUSIONS:

The use of GEMs alone is likely not sufficient for identifying appropriate ICD-10 crosswalks from ICD-9 algorithms, but any algorithm should be reviewed by researchers prior to use in a study. Future research could include the validation of crosswalks after an examination of patient charts.