Free Carnitine (Carnitine Concentration)
This test measures the amount of free carnitine, a compound that helps transport fatty acids into cells for energy production. It’s often checked in conditions affecting metabolism or muscle function.
["Free carnitine helps cells use fat for energy and removes waste products; low levels may signal metabolic or muscle disorders."]
Key facts at a glance
- LOINC
- 53234-1
- Short code
- C0C18R
- Synonyms
- Carnitine Free/C18 DBS-sRto
- Category
- chemistry
- Sample
- serum
- Container
- FDA-approved newborn screening filter paper card (Whatman 903 or equivalent) for dried blood spot collection
- Units
- N/A
- Ref low
- 0
- Ref high
- 0.025
- Critical range
- — – 0.04 N/A
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 0–99 years
- Method
- Tandem mass spectrometry (MS/MS) with electrospray ionization using dried blood spot (DBS) specimen
- CPT
- 82017
- SNOMED
- 44608000
- Specimen volume
- One fully saturated dried blood spot (approximately 75–100 µL whole blood per spot); minimum 3 blood spots required on filter paper
- Stability
- Ambient temperature: stable for 7 days when properly dried; Refrigerated (2–8°C): stable for 30 days; Frozen (-20°C or lower): stable for 1 year. Protect from heat, humidity, and direct sunlight.
- Hemolysis max
- 500
- Lipemia max
- 1000
- Icterus max
- 500
- TAT
- 24–72 hours
- Order
- routine
Why Is This Test Done?
Your doctor may order this test if you have symptoms like muscle weakness, fatigue, or unexplained weight changes. It can also be part of evaluating conditions like mitochondrial disorders, carnitine deficiency, or metabolic syndromes.
What to Expect Before the Test
No special preparation is usually needed, but your doctor may ask you to fast for a few hours before the blood draw. Bring any medications or supplements you take to your appointment.
How the Test Works
A blood sample is taken from a vein in your arm. The sample is sent to a lab where it’s analyzed using a specialized method to measure free carnitine levels.
What the Results Mean
Results are compared to a general reference range for healthy adults. Low levels may indicate a need for further testing or treatment adjustments, while high levels could signal underlying metabolic issues.
Reference range
C0/C18 ratio: <0.025 (normal); 0.025–0.040 (borderline); >0.040 (elevated, suggestive of carnitine palmitoyltransferase II deficiency or other fatty acid oxidation disorder)N/A
No fasting required. For optimal newborn screening results, specimen should be collected between 24–48 hours of life. Avoid contamination of filter paper with milk, formula, or antiseptic solutions. Patient should be on normal diet prior to specimen collection.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
◆Associated findings1
Short name
Free Carnitine
Frequently asked questions
Low free carnitine levels may suggest conditions like primary carnitine deficiency, mitochondrial disorders, or certain genetic metabolic disorders. High levels could be linked to liver disease, diabetes, or other metabolic imbalances. Your doctor will interpret results in the context of your symptoms and medical history.
Low free carnitine can result from genetic disorders, certain medications, kidney disease, or conditions that impair fat metabolism. It may also appear in people with muscle weakness or unexplained fatigue.
If your results are outside the expected range, your doctor may recommend additional tests, such as a carnitine profile (which includes long-chain carnitine) or further evaluation of your metabolic health. They may also adjust medications or suggest dietary changes.
Sources
- 1
- 2Lab Tests OnlineSource
- 3
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.
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