If usual interests or past pleasures are no longer enjoyable and if this condition persists for over two weeks, doctors might suspect a depressive illness. However, other general medical illnesses, such as anemia or an underactive thyroid, may also produce this abnormal state. Therefore, all patients suspected of depressive illness should have a thorough medical examination and review. As yet, there are no objective tests, such as blood analysis or imaging scans, for depressive illness. Diagnosis is made by observing a particular collection of symptoms and disabilities as they have developed over time.
None is sufficient in itself to make the diagnosis.
However, given several such persistent problems, a professional review is needed. Important indicators are lack of energy, becoming socially withdrawn, feeling inadequate, less efficient, inability to concentrate and being indecisive. Some people develop physical complaints that do not respond to medical care. Hopelessness is often associated with severe depression and may pose the risk of suicide. Some depressions are chronic and persistent whereas others may last for months and then improve for no apparent reason.