Early Diagnosis of Neuron Mitochondrial Dysfunction May Reverse Global Metabolic and Neurodegenerative Disease. Global Journal of Medical Research: A Neurology and Nervous System Volume 16 Issue 2 Version 1.0 Year 2016
If I understand your question correctly, I would venture to say yes at this point. I would expect that a direct look at mitochondria and their function in peripheral blood mononuclear cells may provide a better correlative approach than trying to infer by examining plasma proteins. With the specific question posed, however, I don't have direct data to support either approach.
Depends upon what you are looking for...i.e. your outcome measures. Check this paper out, I think it will help https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3076726/