Evaluation of patients with a clinical suspicion of a wide range of inborn errors of metabolism, especially organic acidemias and fatty acid oxidation disorders including primary carnitine deficiency.
Carnitine and its esters are required for normal energy metabolism and serve four primary functions:
- Importing long-chain fatty acids into the mitochondria
- Exporting naturally-occurring short-chain acyl-CoA groups from the mitochondria
- Buffering the ratio of free CoA to esterified CoA
- Removing potentially toxic acyl-CoA groups from the cells and tissues
Evaluation of carnitine in plasma, tissue, and urine identifies patients with primary disorders of the carnitine cycle, as well as disturbances in carnitine levels as a result of organic acidemias and fatty acid oxidation disorders. In the latter disorders, acyl-CoA groups accumulate and are excreted into the urine and bile as carnitine derivatives, resulting in a secondary carnitine deficiency.
Other conditions that are associated with an abnormal carnitine status are neuromuscular diseases, gastrointestinal disorders, familial cardiomyopathy, renal tubulopathies and chronic renal failure (dialysis), and prolonged treatment with steroids, antibiotics (pivalic acid), anticonvulsants (valproic acid), and total parenteral nutrition.
Serum free carnitine: 23 – 53 umol/L
Serum total carnitine: 27 – 63 umol/L
% acylated carnitine: up to 40 % total carnitine
Ref range newborn infants:
Free carnitine: 14.7 +/ – 3.5
Total carnitine: 21.5 +/- 4.5 % Acylated
Royal Victoria Infirmary