Newborn screening by tandem mass spectrometry of the heel stick dried blood spot identifies elevated levels of octanoylcarnitine (C8 acylcarnitine), usually accompanied by decanoyl (C10), hexanoyl (C6) and decenoyl (C10:1) carnitine esters. Also C8/C2 and C8/C10 ratios have been found informative for MCAD. When symptomatic, laboratory examination of blood may reveal hypoglycemia, metabolic acidosis, mild lactic acidosis, hyperammonemia, elevated BUN, and high uric acid levels. Serum transaminases are usually elevated. The urine often shows inappropriately low or absent ketones due to impaired fatty acid oxidation. Low serum and urine carnitines are typically found in the untreated patient. Biochemical testing of blood and urine for carnitine, acylcarnitines, acylglycines, and organic acids is diagnostic for this disorder. A generalized dicarboxylic aciduria is noted, characterized by elevations of suberylglycine and hexanoylglycine. In fibroblasts, the activity of medium chain acyl-CoA dehydrogenase is severely deficient in affected individuals, while heterozygous carriers for the disease usually have intermediate levels of activity, but are otherwise clinically and metabolically unaffected.
Fundamental to the medical management of MCAD is the need to avoid fasting, particularly during periods of high metabolic stress, such as illness. Overnight fasts should be managed with nighttime or late evening feedings where appropriate. The addition of food-grade cornstarch mixed in liquid at bedtime has also helped to decrease the frequency of morning hypoglycemia in some patients. High carbohydrate intake should be encouraged during illnesses, with initiation of intravenous glucose supplementation if the child is unsuccessful in keeping down fluids or unable to take adequate oral feedings.The preventive efficacy of a low fat diet versus a normal fat diet is unclear, but high intake of long and medium-chain fatty acids should be avoided. Supplementation with oral L-carnitine has been associated with a reduction in the frequency and severity of episodes. The continued need for carnitine supplementation post-puberty is uncertain, and has not been adequately studied.