Association Between Patient Health Questionnaire-4 Composite Score and Depression Diagnoses in a Free Clinic Setting: Pooled Cross-sectional Study

This study aimed to examine the predictive validity of the Patient Health Questionnaire-4 (PHQ-4) in identifying depression diagnoses among patients in a student-run free clinic (SRFC) setting. This pooled cross-sectional study utilized electronic health record data from the Equal Access Clinic Network, a network of SRFCs affiliated with the University of Florida. All adult patients who completed PHQ-4 screening questions between October 2015 and February 2020 and had a corresponding ICD-10 diagnostic code were included (n = 2,498). The PHQ-4 composite score, calculated from binary responses to four mental health screening questions, served as the primary independent variable. The primary outcome was provider-diagnosed Major Depressive Disorder (MDD), defined by ICD-10 code F32.9. A multivariable logistic regression model, adjusted for age, sex, race/ethnicity, employment, and marital status, was used to evaluate the association between PHQ-4 scores and provider-diagnosed MDD. Higher PHQ-4 composite scores were significantly associated with increased odds of receiving an MDD diagnosis (adjusted OR = 2.047; 95% CI: 1.830-2.289; p < 0.001). The average PHQ-4 score was 1.17 (SD = 1.47), with 47.2% of patients scoring ≥ 1. Non-White patients, including those identifying as Black or from other underrepresented groups, had significantly lower odds of MDD diagnosis compared to White patients. The PHQ-4 is a strong predictor of MDD diagnoses in a free clinic setting and may serve as an efficient, low-burden screening tool for mental health concerns in underserved populations. Its integration into free clinic settings may support earlier identification and intervention, though disparities in diagnosis across racial and ethnic groups warrant further investigation.