External validation of a prognostic model to improve prediction of psychosis in primary care.

Background Early detection could reduce the duration of untreated psychosis. GPs are a vital part of the psychosis care pathway but find it difficult to detect the early features. An accurate risk prediction tool (P Risk) was developed to detect these. Aim The external validation of P Risk. Methods A retrospective cohort study using a validation dataset of 1,647,934 UK Clinical Practice Research Datalink primary care records linked to secondary care records. The same predictors (age, sex, ethnicity, social deprivation, consultations for suicidal behaviour, depression/anxiety and substance abuse, history of consultations for suicidal behaviour, smoking history and substance abuse and prescribed medications for depression/anxiety/PTSD/OCD and total number of consultations) were used as for P Risk development. Predictive risk, sensitivity, specificity, and likelihood ratios were calculated for various risk thresholds. Discrimination (Harrell's C) and calibration were calculated. Results were compared between the development (GOLD) and validation (AURUM) datasets. Findings Psychosis risk increased with values of the P Risk prognostic index. Incidence was highest in younger age groups and mainly higher in males. Harrell's C was 0.79 (95% CI 0.78, 0.79) in the validation dataset and 0.77 in the development dataset. A risk threshold of 1% gave sensitivity of 65.9% and specificity of 86.6%. Interpretation Further testing is required but P Risk has the potential to be used in primary care to detect future risk of psychosis.