No there is no blood test for confirming diagnosis of depression.  Your psychiatrist is enough for making a diagnosis.  If you have lethargy wt gain etc you can go for thyroid hormone levels but that too is not diagnostic of depression. You may need augmentation of nexito or changing to another antidepressant. Cinvey your suicidal thoughts to your family and doctor.

Of course there tests for thyroid etc but not fir depression.  You can always seek an experts help and understand your issues and resolved by consulting a Psychologist in you city. Relax...

Depression is a clinical diagnosis. There is no such investigation to diagnose depression or for serotonin levels. Serotonin levels are done by researchers as a part of their research work but not by labs for diagnosis. In depressive pts hypothyroidism can co exist but is not diagnostic of depression. If diagnosed with hypothyroidism taking rx for same will also help relieve the symptoms. As for your medication is concerned we need to know how much nexito you are taking and for how long are you taking them ? If your symptoms are not relieved then discuss with your psychiatrist to - : increase the dose :or add another antidepressant :or replace the drug with another antidepressant