Skip to content

Free Carnitine (Carnitine, Free)

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. It may be checked to evaluate metabolic function, especially in conditions affecting fat metabolism.

Quick summary

["Free carnitine helps assess how well your body converts fats into energy."]

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

Key facts at a glance

LOINC
53235-8
Short code
C0C16C18
Synonyms
Carnitine Free/C16+C18 DBS-sRto
Category
chemistry
Sample
serum
Container
Dried Blood Spot (DBS) collection card (Whatman 903 or equivalent filter paper). For serum-based testing, collect in a red-top or serum separator tube (SST).
Units
N/A
Ref low
0.015
Fasting
false
Population
adult
Sex
all
Age range
≥ 0 years
Method
Tandem Mass Spectrometry (MS/MS)
CPT
82017
SNOMED
44608005
Specimen volume
For DBS: At least 3 fully saturated blood spots (approximately 75-100 µL of whole blood per spot). For serum: 1-2 mL of blood in appropriate collection tube yielding 0.5-1 mL serum.
Stability
Dried Blood Spots: Stable for up to 14 days at room temperature, up to 30 days at 2-8°C, and up to 1 year at -20°C or below. Serum: Stable for 7 days at 2-8°C, or 3 months at -20°C. Avoid repeated freeze-thaw cycles.
Hemolysis max
500
Lipemia max
1000
Icterus max
500
TAT
24–96 hours
Order
routine

Why This Test Might Be Ordered

Your healthcare provider may order a free carnitine test if you have symptoms like muscle weakness, fatigue, or unexplained metabolic issues. It’s also used to monitor conditions such as mitochondrial disorders, carnitine deficiency, or certain genetic disorders affecting fat metabolism.

What to Expect Before the Test

No special preparation is usually needed, but you may be asked to fast for a few hours before the blood draw. Avoid strenuous activity or consuming certain supplements (like carnitine) that day, as they could affect results.

How the Test Works

A small sample of blood is drawn from a vein in your arm. The blood is then analyzed in a lab to measure the concentration of free carnitine. The test typically takes a few days for results to return.

What the Results Mean

Results are compared to a reference range, though exact values can vary by lab. Low levels may indicate a deficiency or metabolic disorder, while high levels could suggest conditions like muscle breakdown or certain liver issues.

Reference range

Normal C0/(C16+C18) ratio: ≥ 0.015. Values below this threshold may indicate impaired fatty acid oxidation or carnitine transporter deficiency. Reference values may vary by laboratory.N/A

Specimen: serum

No fasting required. However, patients should avoid carnitine supplementation for at least 24-48 hours prior to specimen collection, as exogenous carnitine can alter the C0 level and affect the calculated ratio. Newborn screening specimens (DBS) are typically collected between 24-72 hours of life.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance

Short name

Free Carnitine

Frequently asked questions

What are the normal reference ranges for this test?
Normal reference ranges can vary by lab and may not be widely standardized. Your healthcare provider will interpret results in the context of your overall health and symptoms. If your levels are outside the expected range, further testing or evaluation may be needed to determine the cause.
Can diet or supplements affect my free carnitine levels?
Yes, diet, certain medications, and supplements (like L-carnitine) can influence results. Avoid consuming high-fat foods or supplements that contain carnitine for a few days before testing to get an accurate reading.
Is this test painful?
The blood draw itself may cause mild discomfort, but it’s generally quick and well-tolerated. Most people experience only a small bruise or slight soreness afterward. If you have a hard-to-reach vein or are prone to bruising, your provider may use a different method.
  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