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Free Carnitine (Serum/Plasma)

Published: August 9, 2026Updated: August 15, 2026

This test measures the amount of free carnitine, a compound that helps transport fatty acids into cells for energy production. Free carnitine levels can be checked to evaluate metabolic function, especially in conditions affecting fat metabolism.

Quick summary

["Free carnitine helps your body use energy efficiently; low levels may signal metabolic issues."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 15, 2026Editorial policy

Key facts at a glance

LOINC
59206-3
Short code
C0C16C18
Synonyms
Carnitine Free/C16+C18 SerPl-sRto
Category
chemistry
Sample
serum
Container
Red-top serum tube (no anticoagulant) or green-top (sodium/lithium heparin) plasma tube; avoid EDTA (chelation interferes with carnitine analysis)
Units
N/A
Ref low
0
Ref high
0.25
Critical range
— – 0.4 N/A
Fasting
false
Population
adult
Sex
all
Age range
0–99 years
Method
Tandem Mass Spectrometry (MS/MS) with electrospray ionization; stable isotope-labeled internal standards
CPT
82017 (Acylcarnitines, quantitative, each specimen); additional CPT codes may apply for ratio calculations and panel components
SNOMED
44608006 (Carnitine measurement); additional SNOMED codes may apply for specific acylcarnitine species and ratio analyses
Specimen volume
0.5–1 mL serum or plasma; minimum 0.2 mL for pediatric or repeat analysis
Stability
Stable for 24 hours at room temperature (15–25°C); 7 days at 2–8°C (refrigerated); up to 3 months at -20°C or below for long-term storage. Avoid repeated freeze-thaw cycles.
Hemolysis max
100
Lipemia max
100
Icterus max
50
TAT
48–168 hours
Order
routine

Why Is This Test Done?

Your healthcare provider may order a free carnitine test if you have symptoms like fatigue, muscle weakness, or unexplained metabolic problems. It’s also used in diagnosing or monitoring conditions such as carnitine deficiency, mitochondrial disorders, or certain inherited metabolic diseases. Sometimes, it’s checked alongside other tests to assess how well your body is processing fats.

What Does the Test Involve?

A blood sample is taken from a vein in your arm. The blood is then sent to a lab where it is analyzed to measure free carnitine levels. No special preparation is usually needed, but you may be asked to avoid certain foods or medications for a few days before the test if instructed by your provider.

What Do Results Mean?

Results can vary depending on your health status and other factors. Low free carnitine levels may indicate problems with fat metabolism, carnitine transport, or mitochondrial function. High levels might be seen in certain metabolic disorders or after certain treatments. Your healthcare provider will discuss the results with you and may recommend further testing or adjustments to your treatment plan.

Common Conditions Monitored

Free carnitine testing is often used to monitor conditions like primary carnitine deficiency, mitochondrial disorders, or metabolic syndromes. It can also help assess how well certain medications or therapies are working for patients with fatty acid metabolism issues.

Reference range

Normal C0/(C16+C18) ratio ≤ 0.25 in healthy individuals. Reference values are age-dependent; pediatric ranges differ from adult ranges. Elevated ratios suggest impaired long-chain fatty acid oxidation.N/A

Specimen: serum

No fasting required. However, results are most interpretable in the fasting or post-absorptive state. Patients should avoid recent high-fat meals or carnitine supplementation prior to collection when possible. Inform the laboratory of any medications or dietary supplements.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance

Short name

Free Carnitine

Frequently asked questions

What causes low free carnitine levels?
Low free carnitine can be caused by genetic disorders that affect carnitine transport, liver disease, kidney problems, or certain medications that interfere with carnitine metabolism. It may also occur in people with mitochondrial disorders or those who have undergone certain surgeries or treatments that disrupt metabolism.
What are the symptoms of abnormal free carnitine levels?
Symptoms of abnormal free carnitine levels can vary widely. Low levels may cause fatigue, muscle weakness, poor growth in children, or problems with energy production. High levels might not cause noticeable symptoms but can sometimes be linked to metabolic imbalances or certain medical conditions. Always discuss symptoms with your healthcare provider.
How often should I get this test?
The frequency of this test depends on your health condition and treatment plan. If you have a known metabolic disorder or are taking medications that affect carnitine levels, your provider may recommend regular monitoring. Otherwise, this test is usually ordered as needed for specific situations or symptoms.
  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 15, 2026. · Read our editorial policy