The diagnostic accuracy of the PHQ-9 in primary care in relation to the presence of single or multiple depression-related risk factors.

BACKGROUND: International guidelines recommend risk-adapted depression screening in primary care. However, empirical evidence on the diagnostic accuracy of depression screening questionnaires in patients at risk for depression remains limited. OBJECTIVE: To evaluate the diagnostic accuracy of the Patient Health Questionnaire-9 (PHQ-9) for detecting major depressive disorder (MDD) in primary care, stratified by the presence of single depression-related risk factors and the amount of risk factors. METHODS: This secondary analysis used data from 985 primary care patients participating in the GET.FEEDBACK.GP trial who completed the PHQ-9, a depression-related risk factor assessment, and underwent evaluation for MDD using the Mini-International Neuropsychiatric Interview (MINI). Accounting for partial verification bias, this study applied an inverse probability weighting normalized for a sample of 985. Sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and the area under the curve (AUC) were calculated for different PHQ-9 cut-off scores across single risk factors and the amount of risk factors. The analysis was pre-registered (https://osf.io/wzctq). RESULTS: Of 985 participants, 89 (9.1%) had a MDD diagnosis. The best-performing PHQ-9 cut-offs, stratified by the amount of risk factors, varied, ranging from 7 to 13, with a higher number of risk factors being associated with a higher best-performing PHQ-9 cut-off score. Sensitivity ranged from 0.78 to 0.99; specificity from 0.80 to 0.91. PPV ranged from 0.40 to 0.88 and NPV from 0.80 to 0.99. AUCs ranged from 0.92 to 0.97, indicating excellent diagnostic accuracy. Similar results were found when stratifying by single risk factors. CONCLUSIONS: The PHQ-9 demonstrated high diagnostic accuracy for detecting MDD in patients at risk for depression. Although optimal cut-offs vary slightly according to the number and type of risk factors present, the findings support the validity of risk-adapted depression screening using the PHQ-9 in primary care.