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Free Carnitine (Serum/Plasma)

Published: August 9, 2026Updated: August 10, 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 assess metabolic health, especially in conditions affecting fat metabolism.

Quick summary

["Free carnitine helps cells use fat for energy and supports overall metabolic function."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 10, 2026Editorial policy

Key facts at a glance

LOINC
32281-8
Short code
C0TRAT
Synonyms
Carnitine Free SFr SerPl
Category
chemistry
Sample
serum
Container
Red-top serum tube (no anticoagulant) or serum separator tube (SST)
Units
N/A
Ref low
0.65
Ref high
1
Fasting
false
Population
adult
Sex
all
Age range
0–999 years
Method
Tandem Mass Spectrometry (MS/MS) or Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS)
CPT
82017
SNOMED
392700009
Specimen volume
1-2 mL of serum; minimum 0.5 mL
Stability
Refrigerated (2-8°C): 7 days; Frozen (-20°C or below): 30 days. Avoid repeated freeze-thaw cycles.
Hemolysis max
100
Lipemia max
50
Icterus max
25
TAT
48–168 hours
Order
routine

Why Is This Test Done?

Your healthcare provider may order a free carnitine 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 sometimes check levels before or after treatments involving medications that affect metabolism.

What Does a Low or High Level Mean?

Low free carnitine levels might indicate a deficiency, which can interfere with how your body uses energy from fats. High levels could suggest an overproduction of fatty acids or certain metabolic conditions. However, results alone don’t diagnose a specific condition—your doctor will consider your symptoms and other test results.

How Is the Test Performed?

A blood sample is drawn from a vein in your arm. The blood is then sent to a lab for analysis. The test measures free carnitine, which is a form of carnitine not bound to other substances in the blood.

What Should You Do Before the Test?

No special preparation is usually needed, but your doctor may advise avoiding certain medications or foods that could affect results. For example, some medications (like certain antibiotics or diuretics) or supplements (like carnitine itself) might influence levels. If you’re unsure, ask your provider.

Reference range

Free carnitine (C0) ratio: 0.65-1.00 of total carnitine. Total carnitine: 38-68 µmol/L (males), 36-67 µmol/L (females). Free carnitine: 25-55 µmol/L (adults). Values vary by age; pediatric and neonatal reference ranges differ significantly.N/A

Specimen: serum

Fasting is not required, but overnight fasting (8-12 hours) is preferred for more accurate results. Avoid recent strenuous exercise prior to specimen collection. Patients should maintain normal dietary habits prior to testing.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Free Carnitine Level

Frequently asked questions

What causes low free carnitine levels?
Low free carnitine can result from genetic disorders that impair carnitine transport, liver or kidney disease, malnutrition, or certain medications that deplete carnitine. It may also appear in people with mitochondrial disorders or those who have undergone certain surgeries or treatments that disrupt metabolism.
What causes high free carnitine levels?
High free carnitine levels can occur in conditions where fat metabolism is overactive, such as uncontrolled diabetes, severe liver disease, or certain types of kidney disease. It may also appear in people with fatty liver disease or those taking medications that affect fat metabolism.
Does this test require fasting?
No, fasting is generally not required for this test. However, your doctor may recommend fasting or other preparations depending on your specific health situation or if other tests are being done simultaneously.
  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 10, 2026. · Read our editorial policy