Diagnosing Addison's disease in its early stages can be challenging. Diagnosis involves assessing blood cortisol levels and, in some cases, performing specific stimulation tests. To differentiate Addison's disease from secondary adrenal insufficiency, blood ACTH (Adrenocorticotropic hormone) levels are examined. It is recommended that these blood tests ideally be conducted between 08:00 and 08:30 AM.