Free Carnitine Urine Rate (24-Hour Collection)
This test measures the amount of free carnitine excreted in your urine over a 24-hour period. Free carnitine is a compound that helps transport fatty acids into cells for energy production.
["Assessing free carnitine levels in urine can help diagnose or monitor conditions affecting fat metabolism."]
Key facts at a glance
- LOINC
- 34259-2
- Short code
- UC0
- Synonyms
- Carnitine Free 24h Ur-sRate
- Category
- chemistry
- Sample
- urine
- Container
- 24-hour urine collection container (3-liter, light-protected, no preservative required for most methods); sterile aliquot tube for final specimen
- Units
- N/A
- Ref low
- 200
- Ref high
- 1200
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 0–99 years
- Method
- Tandem Mass Spectrometry (MS/MS) or Liquid Chromatography-Mass Spectrometry (LC-MS/MS)
- CPT
- 82017
- SNOMED
- 428290009
- Specimen volume
- 10 mL aliquot from a well-mixed 24-hour urine collection
- Stability
- Ambient: 24 hours; Refrigerated (2-8°C): 7 days; Frozen (-20°C or below): 30 days. Avoid repeated freeze-thaw cycles.
- Hemolysis max
- 0
- Lipemia max
- 0
- Icterus max
- 0
- TAT
- 48–168 hours
- Order
- routine
Why This Test Is Done
Your healthcare provider may order this test if you have symptoms or a medical history suggesting a metabolic disorder, such as carnitine deficiency, mitochondrial disorders, or certain genetic conditions that affect how your body uses fats for energy. It can also be used to monitor treatment progress in patients with known metabolic issues.
What to Expect Before the Test
You’ll need to collect all urine produced in a 24-hour period in a special container. Typically, you’ll start the collection in the morning and finish it the same morning the next day. Drink plenty of fluids to ensure adequate urine production, but avoid certain medications or supplements that may interfere with the test results.
What Happens During the Test
No special preparation is required beyond the 24-hour urine collection. The collected urine is sent to a lab for analysis. The lab will measure the concentration of free carnitine in your urine sample.
What the Results Mean
Results are typically reported as the total amount of free carnitine excreted over 24 hours. Abnormal results may indicate an underlying metabolic disorder or other conditions affecting carnitine metabolism. Your healthcare provider will discuss the results with you and may recommend further testing or adjustments to your treatment plan.
Reference range
Reference values vary by laboratory; typically reported in nmol/mg creatinine or μmol/g creatinine. 24-hour excretion rates are age- and sex-dependent. Consult laboratory-specific reference ranges for interpretation.N/A
No special preparation required. Patients should maintain their usual diet prior to collection. Avoid excessive vitamin C supplementation, which may interfere with certain assay methodologies. Inform the laboratory of all medications and supplements being taken.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
Clinical Significance
Frequently asked questions
Low levels of free carnitine in urine may suggest conditions like primary carnitine deficiency, where the body cannot properly transport fatty acids for energy. High levels could be associated with certain metabolic disorders, kidney issues, or other conditions affecting fat metabolism. This test helps guide diagnosis and management of these conditions.
Generally, you should avoid high-fat foods or supplements that may contain carnitine (like some protein or weight-loss supplements) for a few days before the test. However, stick to your usual diet unless instructed otherwise. Always follow specific instructions provided by your healthcare provider or lab technician.
You’ll need to collect all urine produced over a full 24-hour period, starting from one morning and ending the next morning. This includes waking up in the middle of the night to empty your bladder. Make sure to keep the collection container clean and properly labeled.
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