. Author manuscript; available in PMC: 2016 Sep 1.

Published in final edited form as: Genet Med. 2014 Dec 11;17(9):689–701. doi: 10.1038/gim.2014.177

Table 2.

Points to consider regarding mitochondrial biochemical testing in tissue

• Assays of spectrophotometric quantification of OXPHOS enzyme activities differ across various laboratories and make interlaboratory comparison of test results highly variable^159,160

• The use of simultaneous control samples may help validate most ETC test results in muscle¹⁶⁰

• There is little to no margin between patient ranges and control ranges^161,162

• Enzyme activities around the lowest reference value cannot always be “absolutely” normal or abnormal

• Electron transport enzyme activity measures are secondarily affected by many factors, with physical inactivity being relevant to most mitochondrial patients¹⁶³

• ETC analysis may be completely normal in any tissue tested early in the disease process, especially in mitochondrial DNA depletion and deletion syndromes¹⁶⁴

• Interpretation of mitochondrial biochemical testing results is aided by utilizing established diagnostic criteria to avoid mitochondrial dysfunction being identified in a subjective fashion and interphysician variability in diagnoses provided²

ETC, electron transport chain.