There are no specific tests for depression, so your doctor will examine you and do some urine or blood tests to rule out other conditions that have similar symptoms, such as stroke, brain tumour or underactive thyroid. The main way to diagnose depression is by asking you lots of questions about your general health and enquiring about if the way you are feeling is affecting you mentally and physically.
It is important to be open and honest with your doctor. Describing your symptoms and how they are affecting you will really help him/her understand if you have depression and how severe it is. Your doctor will conduct a mental health evaluation and discuss with any family history of bipolar disorder or other mental illnesses. He/she will get a complete history of your symptoms and may also talk to your close relatives or spouse about your symptoms and family medical history.
Depression is often related to other illnesses as well. Anxiety disorders often accompany depression, such as post-traumatic stress disorder (PTSD), obsessive-compulsive disorder, panic disorder, social phobia, and generalized anxiety disorder. Alcohol and other substance abuse or dependence may also co-exist with depression, as well as other serious medical illnesses such as heart disease, stroke, cancer, HIV/AIDS, diabetes, and Parkinson's disease.