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Carnitine (Free and Total) in Serum

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

This test measures the amount of carnitine, a substance that helps move fatty acids into cells to be used for energy. It may be checked to assess metabolism, detect genetic disorders, or evaluate conditions affecting muscle or nerve function.

Quick summary

["Carnitine helps convert fat into energy; low levels may signal metabolic or muscle disorders."]

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

Key facts at a glance

LOINC
40869-0
Short code
C0RAT
Synonyms
Carn esters/C0 SerPl-sRto
Category
chemistry
Sample
serum
Container
Red-top serum tube or serum separator tube (SST); alternatively lithium heparin plasma tube
Units
N/A
Ref low
0.25
Ref high
0.9
Fasting
false
Population
adult
Sex
all
Age range
0–120 years
Method
Tandem Mass Spectrometry (MS/MS) or Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS)
CPT
82017 (Carnitine quantitative, each specimen)
SNOMED
43688007
Specimen volume
1-2 mL of serum or plasma
Stability
Stable for 7 days at 2-8°C; for extended storage, freeze at -20°C or below for up to 3 months. Avoid repeated freeze-thaw cycles.
Hemolysis max
50
Lipemia max
100
Icterus max
50
TAT
72–168 hours
Order
routine

Why This Test Is Done

Your doctor may order this test if you have symptoms like muscle weakness, fatigue, or trouble moving. It could also be part of screening for genetic conditions (e.g., primary carnitine deficiency), metabolic disorders, or to monitor treatment for conditions like heart disease or liver problems. Rarely, it’s checked in people with unexplained muscle pain or nerve issues.

What to Expect Before the Test

No special preparation is usually needed. You may be asked to fast for 8–12 hours before the test if your doctor specifies it, but this isn’t always required. Bring any medications you’re taking, as some may affect results. Avoid strenuous activity or eating high-fat foods for a few days before testing if instructed.

How the Test Is Performed

A blood sample is drawn from a vein in your arm by a healthcare professional. You may feel a small pinch when the needle goes in, but the procedure is quick. The sample is sent to a lab for analysis using a specialized method to measure free and total carnitine levels.

What the Results Mean

Results are compared to a general reference range, but exact values can vary by lab. Low carnitine levels may indicate problems with fat metabolism, muscle breakdown, or certain genetic disorders. High levels could suggest liver disease, kidney issues, or overuse of certain supplements. Your doctor will interpret results in the context of your health and symptoms.

Reference range

Reference range typically 0.25-0.90 for free carnitine ratio; acylcarnitine-to-free carnitine ratio is age-dependent. Consult laboratory-specific reference values. Normal C0 (free carnitine) in serum: 25-65 μmol/L in adults.N/A

Specimen: serum

No special preparation required. Patient should avoid recent strenuous exercise prior to specimen collection. Fasting is not required but overnight fasting may improve diagnostic accuracy for some metabolic conditions.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Carnitine Levels

Frequently asked questions

What might cause low carnitine levels?
Low carnitine levels can result from genetic disorders (e.g., primary carnitine deficiency), certain medications (like some antibiotics or diuretics), liver or kidney disease, or conditions that affect muscle or nerve function. It may also appear in people with untreated heart failure or severe malnutrition.
What might cause high carnitine levels?
High carnitine levels can occur with liver disease, kidney failure, or excessive use of carnitine supplements. Rarely, it may be linked to certain cancers or metabolic syndromes. Your doctor will consider your overall health and other test results to determine the cause.
How often should this test be repeated?
If your results are abnormal, your doctor may repeat the test to confirm findings or check progress with treatment. Frequency depends on your condition—some patients need monitoring every few months, while others may only need it once. Follow your doctor’s advice for follow-up.
  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