Diagnosis

Even with a thorough evaluation, it can sometimes be difficult for your doctor or mental health professional to diagnose seasonal affective disorder because other types of depression or other mental health conditions can cause similar symptoms.

To help diagnose SAD, your doctor or mental health professional may do a thorough evaluation, which generally includes:

• Physical exam. Your doctor may do a physical exam and ask in-depth questions about your health. In some cases, depression may be linked to an underlying physical health problem.
• Lab tests. For example, your doctor may do a blood test called a complete blood count (CBC) or test your thyroid to make sure it's functioning properly.
• Psychological evaluation. To check for signs of depression, your doctor or mental health professional asks about your symptoms, thoughts, feelings and behavior patterns. You may fill out a questionnaire to help answer these questions.
• DSM-5. Your mental health professional may use the criteria for seasonal depressive episodes listed in the Diagnostic and Statistical Manual of Mental Disorders (DSM-5), published by the American Psychiatric Association.