Nonsuicidal self-injury disorder: Does Criterion B add diagnostic utility?

The current paper evaluates Criterion B for Non-Suicidal Self-Injury Disorder, which states that non-suicidal self-injury (NSSI) must occur for at least one function. The majority of individuals who engage in NSSI report at least one function, so it is unclear if Criterion B provides diagnostic utility in individuals who already meet Criterion A (i.e., NSSI occurring on 5 or more days in the past 12 months). This paper compared individuals meeting Criterion A (threshold group) to those with 1-4 acts of NSSI in the past year (subthreshold group) in two different samples. The first sample included 217 undergraduate students, and the second sample included 1082 individuals from a behavioral health hospital, all with past-year NSSI. The majority of both samples reported at least one function of NSSI (99%). For the undergraduate sample, the number of and level of endorsement of functions were similar across threshold and subthreshold groups. For the behavioral health sample, the threshold group endorsed significantly more functions for NSSI and greater endorsement of affect regulation, self-punishment, and toughness compared to the subthreshold group. While some differences were found between NSSI groups, overall endorsement of functions for NSSI appears to be a universal characteristic regardless of NSSI frequency.