The Patient Health Questionnaire (PHQ-9) is a widely used screening tool for major depressive disorder (MDD), although there is debate surrounding its diagnostic properties. For the PHQ-9, we aimed to:

1. Establish the diagnostic performance at the standard cutoff point (10).

2. Compare the diagnostic performance at the standard cutoff point in different clinical settings.

3. Assess whether there is selective reporting of cutoff points other than 10.

We searched three databases — Embase, MEDLINE and PSYCHInfo — and performed a reverse citation search in Web of Science. We selected for inclusion studies of any design that assessed the PHQ-9 in adult populations against recognized gold-standard instruments for the diagnosis of either Diagnostic and Statistical Manual of Mental Disorders or International Classification of Diseases criteria for major depression. Included studies had to report sufficient information to calculate 2*2 contingency tables. Data extraction and synthesis were performed independently by two researchers. For the included studies, we calculated pooled sensitivity, pooled specificity, positive likelihood, negative likelihood ratio and diagnostic odds ratio for cutoff points 7 to 15.

Thirty-six studies (21,292 patients) met inclusion criteria. Pooled sensitivity for cutoff point 10 was 0.78 [95% confidence interval (CI), 0.70–0.84], and pooled specificity was 0.87 (95% CI, 0.84–0.90). At this cutoff, the PHQ-9 is a better screener in primary care than secondary care settings. No conclusions could be drawn at cutoff points other than 10 due to selective reporting of data.

For MDD, the PHQ-9 has acceptable diagnostic properties at cutoff point 10 in different settings. We recommend that future studies report the full range of cutoff points to allow exploration of optimal cutoff points in different settings.