International guidelines recommend routine screening for emotional distress in people with diabetes so that common problems, including depression, can be detected and treated. The 9-item Patient Health Questionnaire (PHQ-9) is a commonly used tool for this purpose. According to its developers, each item corresponds to a diagnostic criterion for depressive disorder from the Diagnostic and Statistical Manual of Mental Disorders 4th Edition (DSM-IV). We query this claim, as item nine does not assess suicidal ideation alone.
The PHQ-9 asks respondents to indicate the frequency with which they experienced the nine diagnostic symptoms of major depressive disorder over the past fortnight (0=not at all; 3=almost every day; total score range: 0-27). Suicidal ideation is defined in the DSM-IV as “recurrent thoughts of death (not just fear of dying), recurrent suicidal ideation without a specific plan, or a suicide attempt or a specific plan for committing suicide”, however, PHQ-9 item nine wording (“thoughts that you would be better off dead or of hurting yourself in some way”) reveals a mismatch with the diagnostic criterion. The item assesses both thoughts of death/suicide and self-harm, without distinguishing between them, and the latter is not a DSM-IV diagnostic criterion for depression.
This poor wording causes interpretation difficulties, as illustrated by Australian and Dutch Diabetes MILES Study data. PHQ-9 data from these studies (N=7019) demonstrates that 10% (n=701) of participants endorsed item nine (score >0) but, of those, 29% (n=206) were not depressed (PHQ-9 total score <10). It seems that many are responding to the “hurting yourself in some way” portion of the item, and are having non-suicidal thoughts of self-harm (e.g. cutting).
Clinicians need to be aware of the limitations of the PHQ-9 so that these can be accounted for when interpreting patient responses, to minimise over-estimation of depressive symptoms and suicidal ideation.