Bi polar cannot be diagnosed through a blood test. Bi polar is diagnosed by going to the Dr. Explaining your symptoms and then the Dr. will usually ask you a list of questions. If you are diagnosed with Bipolar, the Dr. will refer you to a therapist and physciatrist and they will decide which medications work best for you. Bipolar also includes depression, it's a symptom. Here is a link that explains it better. If you'd like to talk more I am here. Just send a message to my inbox. I suffer from bipolar, severe anxiety, multiple personalites, as well panic attacks.
http://psychcentral.com/lib/2007/whats-the-difference-between-bipolar-disorder-and-depression/
Blood work cannot be done to diagnose bipolar. The only way to be diagnosed is to see a psychiatrist and be assessed. There are many drugs used to treat bipolar disorder. Some are Seroquel, Abilify, Lithium, and Risperdal, though there are many more. Depression is just being down and sometimes having a normal time between periods of depression. Bipolar disorder has depressive episodes but also hypomanic or manic episodes. I would suggest going to NAMI.org for more information. It is too complex of a disorder and varies from individual to individual in the experience of it (though it does have the same basic features) to describe in one post. There is a book out there called An Unquiet Mind written by Kay Redford Jamison, as well, and I highly recommend it