The most difficult part of making the diagnosis of depression is considering it in the first place. Unfortunately, a diagnosis of depression is commonly missed. Depressed patients are often hesitant to admit they are not feeling well emotionally. They may describe a number of physical symptoms that their doctor has to evaluate first (with a physical exam and laboratory tests) in order to rule out medical conditions that share some of the symptoms of depression as well as illnesses that may directly cause depression.

Physical Exam and Pertinent History
In order to confirm a diagnosis of depression, the doctor relies on the patient’s medical history for clues. The doctor will certainly ask about the nine classic symptoms of depression (see “What are the Symptoms of Depression?" The doctor should also conduct a general physical exam to search for signs of medical illnesses other than depression that may be associated with changes in sleep patterns, appetite, energy and weight (e.g. hypothyroidism or a low level of thyroid hormone in the body). A thorough neurological exam is also the key to making the diagnosis of depression. Slowing of speech, poor concentration, sluggishness, and restlessness are often related to the depression itself, but they can have medical causes as well.

Laboratory Findings
If the patient's medical history is not complicated, a complete blood count, blood sugar, serum electrolytes, and thyroid function tests will finish the medical evaluation of depression. Patients with specific medical problems may require additional tests. If one suffers from complicated or treatment-resistant depression, further testing may also be required including hepatic (liver) enzymes, vitamin B12 and folate levels, an erythrocyte sedimentation rate, and serology for syphilis and HIV.

Imaging Exams
It is not necessary for all medically healthy patients with normal neurological exams and uncomplicated depression to have CT (Computed Axial Tomography) or MRI (Magnetic Resonance Imaging) scans of the brain. However, if one has a history of head trauma, or if one is experiencing headaches, weakness in one part of the body such as an arm or leg, clumsiness, disorientation, significant memory or concentration deficits, or if one suffers from severe or treatment-resistant depression, a CT or MRI is recommended. These imaging exams will help the doctor determine that other medical problems (i.e. brain tumors, stroke and multiple sclerosis) are not causing the depressive symptoms.