I asked my MD this after my hypochondriac sister swears she was dx with MS after one blood test. this is what I was told.

there are markers in your blood that can measure things like inflammation, and vit D levels which are commonly off in MS patients. Blood work can rule out things that mimic MS like Lupus, Lyme, B12 def and so on, but blood work alone CANNOT rule out, or rule in MS.

MS is a disease that is measured in time and space. 2 attacks that are separate from each other. Means you have to get better, and recover, before you have another attack or flair. MRI is the gold standard as they look for lesions in and around certain areas of the brain. Typically 7 to 10 lesions are required, but with clear sx and additional inflammation markers in the blood tests, they can and do dx based on sx and a lower count. Spinal taps are common to look for Obands.

So, the answer to your question is yes, in that blood work is PART of the puzzle that answers some questions, but NO in that blood work alone cannot and should not be used as the sole critera for a diagnosis.

Clear as mud?