In diagnosing depression, a professional will depend upon observations of a child by family members and other adults involved in her care, as well as her own descriptions of her life.
For a diagnosis of major depressive disorder, a young person will be in a depressed or irritable mood most of the time, or lose interest or pleasure in daily activities most of the time, or both, for at least 2 weeks. These symptoms must be a distinct shift from previous functioning. In addition, she will show a variety of the following signs: marked weight loss or gain; sleeping too much or too little; restlessness or lethargy; fatigue; feelings of worthlessness or excessive or inappropriate guilt; cloudy or indecisive thinking; and a preoccupation with death, plans of suicide, or an actual suicide attempt. A clinician will also need to rule out other causes for these symptoms, including substance abuse, medical conditions like diabetes and hypothyroidism, and other psychiatric disorders. The condition must significantly interfere with her day-to-day activities.