Validation of PHQ-2 and PHQ-9 to screen for major depression in the primary care population.

PURPOSE: Although screening for unipolar depression is controversial, it is potentially an efficient way to find undetected cases and improve diagnostic acumen. Using a reference standard, we aimed to validate the 2- and 9-question Patient Health Questionnaires (PHQ-2 and PHQ-9) in primary care settings. The PHQ-2 comprises the first 2 questions of the PHQ-9.
METHODS: Consecutive adult patients attending Auckland family practices completed the PHQ-9, after which they completed the Composite International Diagnostic Interview (CIDI) depression reference standard. Sensitivities and specificities for PHQ-2 and PHQ-9 were analyzed.
RESULTS: There were 2,642 patients who completed both the PHQ-9 and the CIDI. Sensitivity and specificity of the PHQ-2 for diagnosing major depression were 86% and 78%, respectively, with a score of 2 or higher and 61% and 92% with a score 3 or higher; for the PHQ-9, they were 74% and 91%, respectively, with a score of 10 or higher. For the PHQ-2 a score of 2 or higher detected more cases of depression than a score of 3 or higher. For the PHQ-9 a score of 10 or higher detected more cases of major depression than the PHQ determination of major depression originally described by Spitzer et al in 1999.
CONCLUSIONS: We report the largest validation study of the PHQ-2 and PHQ-9, compared with a reference standard interview, undertaken in an exclusively primary care population. The PHQ-2 score or 2 or higher had good sensitivity but poor specificity in detecting major depression. Using a PHQ-2 threshold score of 2 or higher rather than 3 or higher resulted in more depressed patients being correctly identified. A PHQ-9 score of 10 or higher appears to detect more depressed patients than the originally described PHQ-9 scoring for major depression.