METHODS: HD and ED visits with possible marijuana exposures, diagnoses, or billing codes were identified by the presence of marijuana associated ICD-9-CM codes E854.1, 969.6, 304.3X, and 305.2X in the up to 30 listed discharge codes. The Healthcare Cost and Utilization Project’s Multiple Level Clinical Classification Software was used to categorize the primary diagnoses into 18 categories. Prevalence ratios and 95% confidence intervals (CI) were calculated for each primary diagnosis category in HD and ED visits with possible marijuana exposures, diagnoses, or billing codes compared to HD and ED visits without marijuana associated discharge codes.
RESULTS: The prevalence of the primary diagnosis category mental illness was five-fold higher (PR: 5.07, 95% CI: 5.00-5.14) in ED visits with marijuana associated discharge codes compared to ED visits without marijuana associated discharge codes. The prevalence of primary diagnosis categories of mental illness, injuries and poisonings, and diseases of the nervous system were nine-fold higher (PR: 9.92, 95% CI: 9.84-9.99), 14% higher (PR: 1.14, 95% CI: 1.12-1.16), and 16% higher (PR: 1.16, 95% CI: 1.11-1.21) respectively among HD with marijuana associated discharge codes compared to HD without marijuana associated discharge codes.
CONCLUSIONS: The use of marijuana associated discharge codes does not indicate that marijuana was the primary reason for the visit, but rather the treating physician noted marijuana use. Future coding improvements with ICD-10 codes could elucidate this issue. However, these results support findings from extensive literature reviews published by the Colorado Department of Public Health and Environment regarding associations between marijuana use and injury, and marijuana use and neurological, cognitive and mental health effects. Furthermore, these finding support the need for analysis into which specific diagnoses are driving increases in prevalence ratios of each primary diagnosis category and systematic medical record abstraction to determine whether marijuana use is a plausible explanation for the visits.