The present invention relates to the fields of life sciences and medicine. Specifically, the invention relates to a method for determining a mitochondrial disorder of a subject or predicting a prognosis of a subject having a mitochondrial disorder, wherein the method comprises determining specific biomarkers from a sample of a subject. Also, the present invention relates to a method of selecting a treatment for a subject having a mitochondrial disorder or following up a treatment of a subject having a mitochondrial disorder, wherein the method comprises determining specific biomarkers from a sample of a subject. Still, the present invention relates to a kit comprising tools for determining said specific biomarkers from a sample of a subject and to use of the kit or specific biomarkers of the present invention for determining a mitochondrial disorder of a subject, predicting a prognosis of a subject having a mitochondrial disorder, selecting a treatment for a subject having a mitochondrial disorder or following up a treatment of a subject having a mitochondrial disorder.