A psychometric cut-point to separate emergently suicidal depressed patients from stable depressed outpatients

Context: The design of safe clinical trials targeting suicidal ideation requires operational definitions of what degree of suicidal ideation is too excessive to allow safe participation. Aims: We examined the Scale for Suicide Ideation (SSI) to develop a psychometric cut-point that would identify patients having a suicidal emergency. Settings and Design: The Emergency Department (ED) and the out-patient clinic of a university hospital. Materials and Methods: We used the SSI to contrast 23 stable, depressed adult out-patients versus 11 depressed adult ED patients awaiting psychiatric admission for a suicidal emergency. Statistical Analysis: The performance of the SSI was examined with nominal logistic regression. Results: ED patients were older than out-patients (P<0.001), with proportionally more men (P<0.05), and were more ethnically diverse than the outpatients (P<0.005). Compared to out-patients, ED patients were more depressed (Patient Health Questionnaire-9 score 23.1±3.8 vs. 11.7±7.3, P<0.005) and reported a greater degree of suicidal ideation (SSI scores 25.7±7.3 vs. 4.2±8.4, P<0.0001). Nominal logistic regression for the univariate model of SSI score and group yielded a score of 16 (P<0.0001) as the best cut-point in separating groups, with a corresponding Receiver Operating Characteristic Area Under the Curve = 0.94. Of 34 patients in the total sample, only two were misclassified by SSI score = 16, with both of these being false positive for ED status. Thus, the sensitivity of the cut-point was 100% with specificity of 91%. When the model was expanded to include SSI along with age, gender, ethnicity, sedative-hypnotic use, and over-the-counter use, only SSI score remained significant as a predictor. Conclusions: A SSI score ≥16 may be useful as an exclusion criterion for out-patients in depression clinical trials.