Sorted By Test Name - Mayo Medical Laboratories

CACTS
61194
Carnitine, Urine
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 plasma,
tissue, and urine is a screening test for patients suspected of having 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, 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
1:1,000,000 live births. Collectively, their incidence is approximately 1:1,000 live births.
Primary carnitine deficiency has an incidence of approximately 1:21,000 live births based on Minnesota
newborn screening data. Other conditions which could be indicated by an abnormal carnitine level include
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.
Useful For: 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 Monitoring carnitine treatment
Interpretation: When abnormal results are detected, a detailed interpretation is given, including an
overview of the results and of their significance, a correlation to available clinical information, elements
of differential diagnosis, recommendations for additional biochemical testing and a phone number to
reach one of the laboratory directors in case the referring physician has additional questions.
Reference Values:
FREE
77-214 nmol/mg of creatinine
TOTAL
180-412 nmol/mg of creatinine
RATIO
Acyl to free: 0.7-3.4
Clinical References: 1. Chalmers RA, Roe CR, Stacey TE, et al: Urinary excretion of l-carnitine and
acylcarnitines by patients with disorders of organic acid metabolism: evidence for secondary insufficiency
of l-carnitine. Ped Res 1984;18:1325-1328 2. Scaglia F, Wang YH, Singh RH, et al: Defective urinary
carnitine transport in heterozygotes for primary carnitine deficiency. Genet Med 1998;1:34-39 3. Scaglia
F, Longo N: Primary and secondary alterations of neonatal carnitine metabolism. Semin Perinatol
1999;23:152-161 4. Longo N, Amat di San Filippo C, Pasquali M: Disorders of carnitine transport and the
carnitine cycle. Am J Med Genet C Semin Med Genet 2006;142C(2):77-85 5. Zammit VA, Ramsay RR,
Bonomini M, Arduini A: Carnitine, mitochondrial function and therapy. Adv Drug Deliv Rev
2009;61(14):1353-62
Carnitine-Acylcarnitine Translocase Deficiency, Full Gene
Analysis
Clinical Information: Carnitine-acylcarnitine translocase (CACT) deficiency is a rare autosomal
recessive disorder of fatty acid oxidation. The disease typically presents in the neonatal period with severe
hypoketotic hypoglycemia, hyperammonemia, cardiac abnormalities, hepatic dysfunction, skeletal muscle
weakness, encephalopathy, and early death. However, presentations at a later age with a milder phenotype
have also been reported. Initial screening can be done with plasma acylcarnitines. Definitive diagnosis can
be made by detection of reduced CACT enzyme activity. Mutations in the SLC25A20 gene are
responsible for CACT deficiency, and sequencing of this gene is recommended after positive biochemical
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