I did a MitoSwab mitochondrial function test, which tested mito content and complex I-IV function. I think they'll be adding complex V soon. The company is in PA, and has done work with Children's Hospital of Philadelphia on autistic kids, and dies work with patients with neurodegenerative disorders.
I also consulted with Fran Kendall in Atlanta, who recommended other tests aimed at identifying primary mito disease, including a muscle biopsy, SFN biopsy and nerve conduction test, but a long list of others, too.
The most useful test for me was the GeneDX whole exome sequencing and mtDNA testing. However, you could get the same info, I believe from Dante Labs or Veritas, who ate consumer-oriented. Veritas is dropping their price, I believe.
The other useful testing has been HDRI's nitrotyrosine and nitric oxide test, which indicated that I have high peroxynitrites which can impair complex I and damage mitochondrial membranes. This, paired with a Genova Diagnostics NutrEval, which showed huge oxidative stress, high lipid peroxides, and high 8OHdG, a market of DNA damage, agreed with the researchers findings of high oxidative and nitrosative stress causing peroxynitrite damage, gave my doctors and me a roadmap of how to treat me.
We repeated these tests 9 months later, and my mito function, though still having some problems, dramatically improved, along with my energy, showing the treatment worked. I am continuing treatment and plan to retest in another couple of months.
I am glad I pursued this path - it has been very useful. Feel free to PM me if you have specific questions.