Limitations of PHQ-9 as a first line mental health screener in primary care.

Background: The PHQ-9, originally designed as an assessment for depression, is now widely used as a first line screener in primary care and is often the sole mental health screener used. However, it is currently unknown how well the PHQ-9 performs as a general screener for mental distress. Here we aim to determine the sensitivity and specificity of the (PHQ-9) for capturing general or transdiagnostic mental distress, defined as experiencing 5 or more severe mental health symptoms. Methods: PHQ-9 responses were collected alongside responses to the transdiagnostic Mental Health Quotient (MHQ) assessment that captures 47 symptoms spanning 10 disorders as well as additional elements from RDoC in a sample of 5,750 respondents collected in 2022. PHQ-9 sum scores were compared with those with 5 or more symptoms from the MHQ. Results: At a sum score cut-off corresponding to moderately severe depression, PHQ-9 had low sensitivity, capturing only 46% of those with general mental distress. At a cut-off corresponding to mild depression, sensitivity improved to 93%, while specificity dropped to 57%. Concurrently, the PHQ-9 missed several symptoms that were highly prevalent in the sample population and individuals with Conclusions: Altogether, the PHQ-9, due to its origin as a depression screener, is not appropriate as a screener for general mental distress. In the context of primary care triage, this highlights the need for an alternative disorder agnostic first line screener that enables the identification of severe mental distress regardless of the specific profile of symptoms.