Based on the results obtained in first part of the study, suggesting a significant involvement of the mitochondrial respiratory system in patients with a high degree of renal failure (CKD IV–V) and HD, we measured the protein level of the mitochondrial-encoded subunit I (COXI) and the nuclear-encoded subunit IV (COXIV) of complex IV in the testing-group. Here, COX4I1 is linked to kidney failure.