I would like to have a chromagranin a blood test done. which type of specialist would i be better off going to?

"a blood test": A blood test for chromogranin is far far less valuable than the expertise of a physician who is knowledgeable in the field of interest. Blood tests have false positives and false negatives, and have to be interpreted in the context of the clinical setting. I suggest you see your doctor; if you are worried about a neuroendocrine tumor, then see an endocrinologist or oncologist.