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HomeLaboratory MedicineFree and Total Carnitine

Free and Total Carnitine

Reference Range

Carnitine is a quaternary ammonia water-soluble compound biosynthesized from lysine and arginine. It serves as a mechanism for transport of long-chain fatty acids from the cytoplasm across the inner mitochondrial membrane and into the mitochondrial matrix, the site of b-oxidation of fatty acids for energy generation.

The reference range of carnitine depends on the laboratory being used; various ranges have been reported in the literature.

The following table of values is derived from Belay et al 2006.
These examples do not imply endorsement of the laboratories cited, but instead are used for reference only.

Table. Reference Range of Carnitine at a Single Laboratory
(Open Table in a new window)

Age Range

Serum Free Carnitine (µmol/L)

Serum Total Carnitine (µmol/L)

Neonate

26-76

35-102

Child

41.4±10.4*

56.2±11.4*

Adolescent female

39.3±8.1*

53.2±8.9*

Adolescent male

39.6±9.3*

53.5±10.5*

Adult female

19.3-53.9**

28.1-66.4**

Adult male

38.8-69.5

44.2-79.3

*Mean ± standard deviation (SD)

**95% confidence interval (CI)

Quest Laboratories reports the reference range of total carnitine as follows
:

Men: 30-70 μmol/L

Women: 25-58 μmol/L

Male children (age ≤17 years): 32-62 μmol/L

Female children (age ≤17 years): 28-59 μmol/L

Quest Laboratories reports the reference range of free carnitine as follows
:

Men: 23-59 μmol/L

Women: 19-48 μmol/L

Male children (age ≤17 years): 25-54 μmol/L

Female children (age ≤17 years): 19-51 μmol/L

The University of California San Francisco Laboratory reports the normal values of free and total carnitine in adults as 18-69 μmol/L and 20-71 μmol/L, respectively.

Chace et al (2003) examined free and total carnitine levels in newborns. The reference ranges depended both on technique used (radioenzyme vs tandem mass spectroscopy) and the sample type (whole blood vs serum).

Variations in the ratio of free to total carnitine may also be important; typically, normal is reported as 0.1-0.4.

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