What exactly does a blood serotonin level do in the body? can ssris mess with the blood levels?

Its a brain chemical: Ssri's change the amount of serotonin in the brain. When your brains levels of serotonin and other chemicals are in balance, your brain gets healthy, allows normal sleep, controls pain better, and even performs intelligence tests better. Depression is a disease that can shrink the brain size and function, but usually responds to ssri's in 6 weeks.

Depends: A few functions of serotonin: 1) serotonin decreases appetite, 2) serotonin makes the gut move faster, 3) serotonin helps regulate aging, learning, and memory, 4) serotonin regulates bone metabolism. Ssris increase the level of serotonin in the synaptic cleft available to bind to the postsynaptic receptor. By so doing it treats clinical depression. See a doctor to check your serotonin level.

Blood Serotonin: Blood serotonin may differ from the amount available in the brain, because of the blood-brain barrier. Blood or serum serotonin (not CSF serotonin) can be measured to look for carcinoid syndrome, where a tumor secretes the neurochemical, serotonin. These tumors are rare, and most are in the GI tract. Symptoms include diarrhea, flushing, intermittent belly pain, and low blood pressure.