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Free Carnitine (Serum)

Published: August 9, 2026Updated: August 16, 2026

This test measures the amount of free carnitine, a compound that helps transport fatty acids into cells for energy production.

Quick summary

["Free carnitine helps assess how well your body is using fats for energy and can indicate metabolic health."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 16, 2026Editorial policy

Key facts at a glance

LOINC
110537-8
Short code
C0U
Synonyms
Carnitine Free Msmt Ur
Category
chemistry
Sample
urine
Container
Sterile, leak-proof urine collection container; preferably a 24-hour urine container with preservative if timed collection is required
Units
N/A
Ref low
0
Ref high
15
Fasting
false
Population
adult
Sex
all
Age range
0–120 years
Method
Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS)
CPT
82040
SNOMED
271777001
Specimen volume
10 mL random urine or complete 24-hour urine collection (approximately 1500-2000 mL)
Stability
Refrigerated (2-8°C): 7 days; Frozen (-20°C or below): 30 days. Avoid repeated freeze-thaw cycles.
Hemolysis max
0
Lipemia max
0
Icterus max
0
TAT
48–168 hours
Order
routine

Why This Test Might Be Ordered

Your healthcare provider may order this test if you have symptoms of metabolic disorders, such as muscle weakness, fatigue, or unexplained weight changes. It may also be used to monitor conditions like mitochondrial disorders, carnitine deficiency, or certain genetic metabolic diseases. Doctors might also check it in patients with liver disease, kidney disease, or those on certain medications that affect carnitine levels.

What to Expect Before the Test

No special preparation is usually needed, but you may be asked to fast for 8–12 hours before the test if it’s drawn from serum. If you’re taking medications that could affect carnitine levels (like some antibiotics or diuretics), let your provider know. Avoid strenuous activity the day of the test.

How the Test Is Performed

A blood sample is drawn from a vein in your arm by a healthcare professional. The blood is then processed to separate serum for analysis. Free carnitine is measured using a specialized laboratory technique, often involving chromatography or immunoassay.

What the Results Mean

Results are typically reported as a concentration in micromoles per liter (µmol/L). Low levels may suggest carnitine deficiency, metabolic disorders, or conditions affecting fat metabolism. High levels could indicate liver disease, kidney problems, or certain genetic disorders. Your provider will interpret results in the context of your overall health and symptoms.

Reference range

Reference values vary by laboratory; typically expressed as mmol/mol creatinine or μmol/g creatinine. Normal urinary free carnitine excretion is generally <15 mmol/mol creatinine in adults.N/A

Specimen: urine

No special preparation required. Patients should maintain normal diet and hydration prior to collection. Avoid strenuous exercise before specimen collection. Dietary intake of carnitine (red meat, dairy) may affect results.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance

Short name

Free Carnitine

Frequently asked questions

What could cause low free carnitine levels?
Low free carnitine levels may be linked to conditions like primary carnitine deficiency, mitochondrial disorders, or certain genetic mutations. It can also occur in people with liver disease, kidney disease, or those on medications that deplete carnitine. Symptoms like muscle weakness, fatigue, or heart issues may accompany low levels.
What could cause high free carnitine levels?
Elevated free carnitine can result from liver disease, kidney failure, or certain metabolic disorders. It may also appear in people with uncontrolled diabetes or those taking medications that affect fat metabolism. High levels alone don’t always indicate a problem, but they warrant further evaluation.
How often should this test be repeated?
Your provider will determine how often to repeat this test based on your symptoms, diagnosis, and treatment plan. If you have a known metabolic disorder or ongoing health concerns, follow-up may be scheduled every few months or as needed to monitor changes in your levels.
  1. 1
    MedlinePlus — Laboratory TestsSource
  2. 2
    Lab Tests OnlineSource
  3. 3
    Mayo Clinic — Tests & ProceduresSource

Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.

This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.

Medical Disclaimer

This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.

If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.

Medically reviewed by WellAlly Editorial Team Last reviewed August 16, 2026. · Read our editorial policy