Is serotonin levels checked on a full blood count if not what would a doctor tick on a blood test form to check serotonin levels ?

Serotonin level: A hematology blood count measures things like amount of hemoglobin, number & size of red & white blood cells, platelets, etc. Serotonin level would not normally be a part of this, and another blood sample would need to be drawn. "serotonin level" may be tested via serum or 24-hour urine collection. The latter is often used in a workup for tumors that secrete serotonin or related metabolites.