Increased very long chain fatty acids in patients on a ketogenic diet: a cause of diagnostic confusion.

We found an elevation of very long chain fatty acids in 13 of 22 plasma samples from patients on a ketogenic diet for the treatment of uncontrolled seizures. Because elevated values of very long chain fatty acids are a biochemical manifestation of peroxisomal dysfunction, this phenomenon might lead to diagnostic confusion. Thus the history and clinical status should be considered when plasma levels of very long chain fatty acids are interpreted.