Clinical Information

Carnitine and its esters are required for normal energy metabolism and serve 4 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 serum, plasma, tissue, and urine screens patients for suspected primary disorders of the carnitine cycle, or secondary 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. More than 100 such primary and secondary disorders have been described. Individually, the incidence of these disorders varies from <1 in 10,000 to >1 in 1,000,000 live births. Collectively, their incidence is approximately 1 in 1,000 live births. Primary carnitine deficiency has an incidence of approximately 1 in 21,000 live births based on Minnesota newborn screening data.

Other conditions which could cause an abnormal carnitine level 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.

Follow-up testing is required to differentiate primary and secondary carnitine deficiencies and to elucidate the exact cause.