A diagnosis is made via a medical professional’s evaluation and tests to identify disorders than can cause depression.
A medical professional is usually able to diagnose depression based on symptoms. They use specific lists of symptoms (criteria) to diagnose the different types of depressive disorders.
To help distinguish depression from ordinary changes in mood, medical professionals determine whether the symptoms are causing significant distress or are impairing an individual’s ability to function. A previous history of depression or a family history of depression helps confirm the diagnosis.
Excessive worrying, panic attacks, and obsessions are common in depression and may lead the medical professional to incorrectly think that the individual has an anxiety disorder.
In older individuals, depression may be difficult to notice, especially if they do not work or have little social interaction. Also, depression may be mistaken for dementia because it can cause similar symptoms, such as confusion and difficulty concentrating and thinking clearly. However, when such symptoms are caused by depression, they resolve when depression is treated. When dementia is the cause, they do not resolve.
Standardised questionnaires are used to help identify depression and determine how severe it is, but they cannot be used alone to diagnose depression. Two such questionnaires are:
- The Hamilton Depression Rating Scale, conducted verbally by an interviewer; and
- The Beck Depression Inventory, a self-administered questionnaire.
- For older people, there is a Geriatric Depression Scale questionnaire.
Medical professionals also ask individuals whether they have any thoughts or plans to harm themselves. Such thoughts indicate that depression is severe.
Currently, no test can confirm depression.
However, laboratory tests may help a medical professional determine whether depression is caused by a hormonal or other physical disorder.
For example, blood tests are usually done to detect a thyroid disorder or vitamin deficiency. In younger individuals, tests may be done to detect drug abuse.
A thorough neurological examination is done to check for Parkinson disease, which causes some of the same symptoms.
Individuals who have severely disturbed sleep may need to have testing (polysomnography) to distinguish sleep disorders from depression.