Understanding Your Diagnostic Lab Test: What It Is, Why It Matters, and What to Expect
This blood test measures the ratio of acylcarnitine to free carnitine (C0) to help detect certain metabolic disorders.
{"The test measures carnitine levels in the blood to check metabolic function","It helps screen for inherited metabolic disorders affecting fatty acid oxidation","A small blood sample is collected, usually from a finger prick or heel stick","Abnormal results may indicate problems with how the body converts fat into energy","Follow-up testing is often needed if results are abnormal"}
Key facts at a glance
- LOINC
- 59249-3
- Short code
- AC/C0 Ratio
- Synonyms
- Acylcarnitine/Acyl+C0 DBS-sRto
- Category
- chemistry
- Sample
- serum
- Container
- Dried Blood Spot (DBS) filter paper collection card
- Units
- N/A
- Ref low
- 0.02
- Ref high
- 0.25
- Critical range
- — – 0.5 N/A
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- ≥ 0 years
- Method
- Tandem Mass Spectrometry (MS/MS)
- CPT
- 82017
- SNOMED
- 122269009
- Specimen volume
- 3-4 complete spots (approximately 100-120 μL blood total)
- Stability
- Room temperature: 7 days; Refrigerated (2-8°C): 14 days; Frozen (-20°C): 30+ days
- Hemolysis max
- 500
- Lipemia max
- 1000
- Icterus max
- 500
- TAT
- 24–72 hours
- Order
- routine
This test is a laboratory procedure that helps your doctor evaluate your health by measuring specific substances or markers in a sample from your body, such as blood or urine, in order to detect a medical condition, monitor an existing diagnosis, or screen for problems before symptoms appear.
The acylcarnitine to free carnitine (C0) ratio test is a blood test that measures the balance between two forms of carnitine in your blood. Carnitine is a substance that helps your body turn fat into energy. This test is often used as part of newborn screening programs to detect certain metabolic disorders that affect how the body processes fatty acids.
This test is important because it can reveal early signs of disease, confirm or rule out a diagnosis, guide your doctor's treatment decisions, and help track how well a therapy is working over time, allowing health problems to be addressed promptly and reducing the risk of complications.
Carnitine plays a crucial role in energy production. Free carnitine (C0) helps transport fatty acids into cells where they are burned for energy. Acylcarnitines are created when carnitine binds to fatty acids. The ratio between these two forms helps doctors understand if the body's energy production system is working properly. An abnormal ratio may suggest metabolic disorders such as carnitine transport defects or fatty acid oxidation disorders.
The test is usually performed by a trained healthcare professional who collects a small sample, such as blood drawn from a vein in your arm or a urine specimen, which is then sent to a laboratory for analysis; the procedure is typically quick, requires no special preparation unless your doctor advises otherwise, and causes only minimal, temporary discomfort.
A healthcare professional will collect a small blood sample, typically from a finger prick or heel (in newborns). The blood is then analyzed in a laboratory to measure the levels of acylcarnitine and free carnitine, and calculate their ratio. The test is often part of a larger newborn screening panel.
Reference range
Acylcarnitine/Carnitine Free (C0) ratio: 0.02-0.25 (varies by laboratory methodology and reference population)N/A
No fasting required. Test is typically collected as part of routine newborn screening 24-72 hours after birth. For non-newborn patients, no special preparation required.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
This test is primarily used to screen for inherited metabolic disorders, particularly those affecting fatty acid oxidation. Normal ratios indicate proper carnitine metabolism and energy production from fats. Abnormal ratios may suggest conditions such as primary carnitine deficiency, multiple acyl-CoA dehydrogenase deficiency, or other fatty acid oxidation disorders. These conditions can lead to serious health problems if not detected and treated early, including muscle weakness, heart problems, and metabolic crises. Treatment often involves dietary modifications and carnitine supplementation.
Frequently asked questions
Do I need to fast before this test?
Is this test painful?
What do abnormal results mean?
How long does it take to get results?
Is treatment available if a disorder is detected?
Sources
- 1
- 2
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