Diagnosing SAD involves more than just noticing you feel a bit “off” in the winter.
It’s a clinical diagnosis, meaning it follows specific criteria used by mental health professionals, most commonly those in the DSM-5 (Diagnostic and Statistical Manual of Mental Disorders, 5th Edition).
It isn’t a standalone diagnosis. Not only that, but it’s classified as a specifier for major depressive disorder (MDD) or bipolar disorder, meaning the depression occurs in a seasonal pattern.
To meet the diagnostic criteria, a person must:
- Meet criteria for a major depressive episode
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- At least 5 symptoms (low mood, fatigue, sleep issues, loss of interest) lasting for 2+ weeks.
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- Symptoms cause noteworthy distress or impairment.
- Seasonal pattern
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- Depressive episodes occur at the same time of year (usually fall or winter).
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- Full remission or change to mania/hypomania occurs in a specific season (typically spring/summer).
- Repetition over time
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- This seasonal pattern has happened for at least 2 consecutive years.
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- More seasonal episodes than non-seasonal ones throughout the person’s lifetime.
- No better explanation
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- Symptoms aren’t better explained by seasonal stress, such as job loss around the holidays, for instance.
Additional diagnostic tools
While there’s no blood test or scan for SAD, clinicians often use:
- Structured clinical interviews (e.g., MINI, SCID).
- Self-report questionnaires like:
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- SIGH-SAD (Structured Interview Guide for Hamilton Depression Rating Scale – Seasonal Affective Disorder Version).
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- Seasonal Pattern Assessment Questionnaire (SPAQ).
Widely used but less reliable for formal diagnosis.
- Rule-outs for:
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- Thyroid issues (e.g., hypothyroidism).
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- Anemia.
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- Vitamin D deficiency.
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- Other psychiatric disorders like dysthymia and bipolar disorder.
- Differential diagnosis (what SAD might be mistaken for):
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- Major depression (non-seasonal).
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- Bipolar II disorder (particularly if depressive episodes occur in winter and hypomania in summer).
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- Dysthymia (persistent mild depression).
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- Vitamin D or iron deficiency, which can mimic fatigue symptoms.
Why is it often underdiagnosed?
SAD is often underdiagnosed because many people think feeling tired or down in winter is just “normal.”
For example, while I always feel a bit more weary around that time, it’s certainly not as bad as when I was suffering from severe acute depression.
But it’s worth seeking treatment if symptoms interfere with daily life and recur each year.
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