Construction of a register-based severity index for anorexia nervosa in Denmark: Association with overall and cause-specific mortality.

Background: Considering the high likelihood of chronicity, it is imperative to understand the risk factors and outcomes associated with severe anorexia nervosa (AN), for which Danish registers provide a unique opportunity. We developed a measure of AN severity adapted from clinical literature for use in register-based research.

Methods: The study population included all Danish individuals born between 1963 and 2007 who were diagnosed with AN from 1969 to 2013. Using register data, we constructed the anorexia nervosa register-based severity index (AN-RSI), incorporating early or late illness onset, number of inpatient admissions and outpatient treatments, cumulative treatment length, and illness duration, each weighted based on clinical importance. Associations between AN-RSI scores, evaluated 5 years after first AN diagnosis, and mortality were estimated using survival analysis.

Results: Among 9167 individuals diagnosed with AN, 132 died during follow-up: 17 from AN, 30 from suicide, and 85 from other causes. Higher AN-RSI scores were associated with increased rates of mortality from AN, somatic anorexia diagnosis, suicide, alcohol-related causes, and any cause. AN cases who scored in the top 20% of AN-RSI had especially high mortality rates. Furthermore, severe AN cases were also more likely to be in treatment in the next 5 years after severity was established.

Conclusions: AN-RSI effectively captures mortality and long-term treatment in the absence of detailed patient records and is associated with later mortality in AN patients. AN-RSI could serve as a tool to examine epidemiological and genetic risk factors associated with AN course and outcomes.