There are no blood tests done to diagnose MS.
Rather, the blood tests are done to determine if there is some other cause(s) for various symptoms.
Many diseases and disorders look alike from the outside. They share symptoms. Lots of things can be mistaken for MS. So doctors generally do blood tests to rule out things like infections in the body, or rheumatological disorders, or thyroid, diabetes, stuff like that. If they find those kinds of issues, then there are treatments for some of those problems. If they don't -- then they'll look even more closely at things like MS. With all the things you say you've already been diagnosed with, I'd guess that the doctors you're seeing have already run all the appropriate blood testing, to come to those diagnoses.
...I am not a doctor, nor health professional, and don't pretend to be one, here.....