Estimating the risk of PTSD in recent trauma survivors: results of the International Consortium to Predict PTSD (ICPP)

Abstract

A timely determination of the risk of post-traumatic stress disorder (PTSD) is a prerequisite for efficient service delivery and prevention. We provide a risk estimate tool allowing a calculation of individuals' PTSD likelihood from early predictors. Members of the International Consortium to Predict PTSD (ICPP) shared individual participants' item-level data from ten longitudinal studies of civilian trauma survivors admitted to acute care centers in six countries. Eligible participants (N=2,473) completed an initial clinical assessment within 60 days of trauma exposure, and at least one follow-up assessment 4-15 months later. The Clinician-Administered PTSD Scale for DSM-IV (CAPS) evaluated PTSD symptom severity and diagnostic status at each assessment. Participants' education, prior lifetime trauma exposure, marital status and socio-economic status were assessed and harmonized across studies. The study's main outcome was the likelihood of a follow-up PTSD given early predictors. The prevalence of follow-up PTSD was 11.8% (9.2% for male participants and 16.4% for females). A logistic model using early PTSD symptom severity (initial CAPS total score) as a predictor produced remarkably accurate estimates of follow-up PTSD (predicted vs. raw probabilities: r=0.976). Adding respondents' female gender, lower education, and exposure to prior interpersonal trauma to the model yielded higher PTSD likelihood estimates, with similar model accuracy (predicted vs. raw probabilities: r=0.941). The current model could be adjusted for other traumatic circumstances and accommodate risk factors not captured by the ICPP (e.g., biological, social). In line with their use in general medicine, risk estimate models can inform clinical choices in psychiatry. It is hoped that quantifying individuals' PTSD risk will be a first step towards systematic prevention of the disorder.

Keywords: Post-traumatic stress disorder; clinician-administered PTSD scale for DSM-IV (CAPS); exposure to prior interpersonal trauma; female gender; lower education; prediction; prevention; risk assessment tool; trauma survivors.

Figure 1

Histogram of participants’ baseline PTSD symptoms severity scores (CAPS₀ total scores). Dots represent individual participants; overlayed triangles those who subsequently developed PTSD. PTSD – post‐traumatic stress disorder, CAPS₀ – baseline score on Clinician‐Administered PTSD Scale for DSM‐IV.

Figure 2

Predicted probabilities of endpoint PTSD conditional on initial (CAPS₀) severity scores. The dots represent the raw conditional probability of PTSD at follow‐up given the CAPS₀ score, smoothed with a kernel of width 5. The solid black line represents the logistic model predicted probability given the CAPS₀ score. The gray area is the 95% confidence interval for the prediction model. The dashed line represents the prediction function derived from participants with follow‐up observations later than 9 months. PTSD – post‐traumatic stress disorder, CAPS₀ – baseline score on Clinician‐Administered PTSD Scale for DSM‐IV.