There’s no test unfortunately. Typically, if your stutter is sensitive to dopamine swings, then substances like caffeine or sugar will exacerbate your stuttering, like it does for me. If you find caffeine/sugar actually makes you feel more fluent from the dopamine boost, then you could potentially have a lower dopamine baseline. Like people with ADHD. So, there’s no blood test to check. You just need to see what improves or worsens your stutter and go from there.