Only a doctor can diagnose clinical depression. The illness is distinguished by overwhelming feelings of sorrow, loneliness and hopelessness that are often accompanied by physical symptoms, says WebMD.
Feelings of sadness are normal for everyone, but clinical depression occurs when these feelings are so strong and persistent that they disrupt a person's ability to conduct everyday tasks. Some symptoms of clinical depression are fatigue, feelings of worthlessness or guilt, insomnia or excess sleeping, loss of interest in activities that were once enjoyed, and difficulty concentrating, according to WebMD. Other symptoms are irritability, unexplained aches and pains, digestive issues not caused by other conditions, and thoughts of suicide or self harm.
Depression can be diagnosed through lab tests, physical exams and psychological evaluations, notes Mayo Clinic. Blood tests can screen for abnormal thyroid function, which can contribute to depression. During a physical exam, a doctor can check for underlying health issues that may be causing the depression. To determine the cause of a patient's depression, a doctor may ask questions about family history and alcohol or drug use. He may also want to know when the feelings of depressions first began. Patients should be honest in answering all of their doctor's questions for the best chance of an accurate diagnosis.