Quick answer
There's no lab test for depression, but validated screening questionnaires like the PHQ-9 measure depression symptoms and severity. These are widely used to screen for depression and track it, and are often paired with anxiety screens since the two frequently co-occur. Diagnosis, though, requires a professional assessment.
Screening tools for depression
While depression can't be diagnosed by a blood test or scan, validated questionnaires measure it effectively. The most widely used is the PHQ-9 (Patient Health Questionnaire 9-item), which asks about common depression symptoms over the past two weeks — low mood, loss of interest or pleasure, changes in sleep and appetite, fatigue, concentration difficulties, feelings of worthlessness, and thoughts of self-harm — and produces a severity score. Shorter versions (like the PHQ-2) exist for quick screening. These are standard tools in healthcare for screening for depression, gauging its severity, and monitoring change over treatment.
Why it's relevant to anxiety
You'll often encounter depression screening in the context of anxiety, because the two frequently co-occur — many people experience both anxiety and depression together. Clinicians commonly screen for both (often pairing the PHQ-9 for depression with the GAD-7 for anxiety), since understanding whether depression accompanies anxiety matters for treatment and can change the approach. So even if your main concern is anxiety, you might be asked depression-screening questions as part of building a complete picture. If you have anxiety, it's genuinely worth being aware of depression too, given how often they travel together.
What tests can and can't do
Depression questionnaires are validated, useful tools for screening and measuring severity — but they aid assessment rather than diagnose. A raised score suggests depression is likely and warrants professional evaluation, which is what actually diagnoses and guides treatment. Importantly, these tools include questions about thoughts of self-harm — and this is where a note of care matters: if you're experiencing thoughts of harming yourself or that life isn't worth living, please reach out for support right away, whether to a doctor, a crisis line, or someone you trust; these feelings are treatable, and you don't have to face them alone. More generally, if a depression (or anxiety) screen suggests you're struggling, treat it as a prompt to seek proper help — both depression and anxiety are very treatable, and reaching out is the first step toward feeling better.
What tests can and can't do
Screening questionnaires are conversation starters, not verdicts. A high score means 'worth discussing with a professional,' and a low score doesn't invalidate your struggle. Only a qualified clinician can diagnose an anxiety disorder — and a diagnosis is a doorway to help, not a label that defines you.
This article is for general information only and is not medical advice, diagnosis, or treatment. Always consult a qualified health professional about your situation. If you are in crisis, contact your local emergency number or a crisis line immediately.