A "Patch" to the NYU Emergency Department Visit Algorithm.

Objective: To document erosion in the New York University Emergency Department (ED) visit algorithm's capability to classify ED visits and to provide a "patch" to the algorithm.

Data Sources: The Nationwide Emergency Department Sample.

Study Design: We used bivariate models to assess whether the percentage of visits unclassifiable by the algorithm increased due to annual changes to ICD-9 diagnosis codes. We updated the algorithm with ICD-9 and ICD-10 codes added since 2001.

Principal Findings: The percentage of unclassifiable visits increased from 11.2 percent in 2006 to 15.5 percent in 2012 (p < .01), because of new diagnosis codes. Our update improves the classification rate by 43 percent in 2012 (p < .01).

Conclusions: Our patch significantly improves the precision and usefulness of the most commonly used ED visit classification system in health services research.