Is there a way to measure what neurotransmitters (and in what amount) are present in a person via blood or other method? I feel like if such information was available there could be experiments regarding the tracking and treatment of many mental disorders, but most specifically Bipolar Disorder. For example, if there could be an established "norm" of neurotransmitter levels you could then find the levels a person has and alter them via a mixture of drugs and monitor the levels periodically. This wouldn't require MRI imaging because you wouldn't be tracking when the neurotransmitters were triggered but the levels, the triggering/action potentials would be changed through cognitive behavioral and dialectal behavioral therapy. This is a alight ramble but i would appreciate any thoughts or insight.
I am not from a pure field of neuroscience so I did a bit of research. (Part put in bold by me is the bit which pertains to Bipolar Disorder (BPD))
While catecholamines and serotonin in the blood and urine are not derived from the brain sometimes, for reasons that are not known, they do reflect brain levels. For example, urinary dopamine is low in Parkinson's disease (Barbeau, Murphy & Sourkes, 1961) even though urinary dopamine levels are thought to be derived mainly from dopamine formation in the kidney. However, urinary dopamine is not a diagnostic test for Parkinson's disease. There are many papers that measured serotonin related compounds in blood or plasma in psychiatric disorders and there is evidence that sometimes there can be a correlation between blood, or plasma, and brain measures (Yan, et. al. 1993).
The Lundbeck Institute's Brain Explorer website explains that studies of serotonin receptors show "substantial evidence for the role of serotonin in patients with bipolar disorder." Research about serotonin and the way it is metabolized indicates a reduced concentration of serotonin metabolites in bipolar disorder patients (Source).
A quick Google Scholar search for "bipolar disorder and serotonin" produces a list of many studies including:
For the bit I do know a bit about, treatment for problems with serotonin levels include SSRIs — Fluoxetine, Paroxetine or Sertraline for example — which work by increasing serotonin levels in the brain.
López-Figueroa, A. L., Norton, C. S., López-Figueroa, M. O., Armellini-Dodel, D., Burke, S., Akil, H., ... & Watson, S. J. (2004). Serotonin 5-HT1A, 5-HT1B, and 5-HT2A receptor mRNA expression in subjects with major depression, bipolar disorder, and schizophrenia. Biological psychiatry, 55(3), 225-233.
Mundo, E., Walker, M., Cate, T., Macciardi, F., & Kennedy, J. L. (2001). The role of serotonin transporter protein gene in antidepressant-induced mania in bipolar disorder: preliminary findings. Archives of general psychiatry, 58(6), 539-544.
Rees, M., Norton, N., Jones, I., McCandless, F., Scourfield, J., Holmans, P., ... & Redman, K. (1997). Association studies of bipolar disorder at the human serotonin transporter gene (hSERT; 5HTT). Molecular psychiatry, 2(5), 398.
Yan, D., Urano, T., Pietraszek, M. H., Shimoyama, I., Uemura, K., Kojima, Y., ... & Takada, A. (1993). Correlation between serotonergic measures in cerebrospinal fluid and blood of subhuman primate. Life sciences, 52(8), 745-749.
DOI: 10.1016/0024-3205(93)90237-W PMID: 7680408