The standard for diagnosis of depression in the United States is the American Psychiatric Association's Diagnostic and Statistical Manual of Mental Disorders (DSM-III). To ascertain which DSM criteria patients meet and to assess their symptoms, psychiatrists often rely on psychodiagnostic instruments such as the Beck Depression Inventory, the Zung Self-Rating Depression Scale, the Hamilton Depression Rating Scale, and the Schedule for Affective Disorders and Schizophrenia.
Unfortunately, clinicians cannot yet base diagnoses on the results of objectively assessed physiological abnormalities (other than superficially observable phenomena, such as anorexia, psychomotor retardation, and early morning waking in some types of depression).
Hence the quest for definitive biological "marker systems" continues. Perhaps the best-known system at present is the dexamethasone suppression test. On this assay, exogenous dexamethasone administration fails to suppress endogenous cortisol secretion in many different disease states, including some depressions. Another is the urinary assay for the major norepinephrine metabolite, 3-methoxy-4-hydroxyphenylglycol. Others