No objective tests are available for depression. Some tests used in research protocols examine levels of certain stress hormones or look at brain functioning. These are research based only, however, and have no utility in clinical practice. Your doctor may order blood tests to check for any underlying conditions that may mimic depression such as low thyroid hormone. Blood tests or electrocardiograms may be ordered for baseline purposes, depending on the medication that is to be prescribed, because some medications may have effects on certain organ systems in the body.
Although not a required part of an evaluation, some clinicians use various rating scales and self-report forms to assist in the evaluation process. Scales may be useful in tracking the progression of the depression in a quantifiable way. Comprehensive diagnostic scales can guide the clinician in going through a differential diagnostic process to exclude other causes for the symptoms before establishing a diagnosis. Such scales may indeed establish a diagnosis of a depression, but they are based on the same clinical criteria used with-out a scale. These scales are mostly useful in research to establish reliability in diagnosis and to increase the validity of the study.