Blood draw
Carnitine Differentiation
Carnitine fraction profile; fatty acid metabolism.
€ 116,00
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Vitamins, minerals and amino acids · Blood
Acylcarnitine
The carnitine that is bound to fatty acid or amino acid residues; a profile of it is part of metabolic testing.
At a glance
- Measured in blood
- In 1 test panel
- No special preparation
Explanation
Acylcarnitine: what is measured?
As soon as carnitine picks up a fatty acid to carry it into the mitochondria, it is called acylcarnitine. There are dozens of types, which differ in the length of the bound fatty acid. If one of the enzymes that break down fatty acids does not work properly, one particular type of acylcarnitine builds up. A laboratory therefore usually measures a whole profile of individual acylcarnitines; the part of the newborn heel prick that looks for fatty acid and amino acid disorders is based on the same principle. A single total value is the sum of all these types together.
What can it detect?
- A sign that fatty acids are not being broken down properly, with the pattern showing which step is failing
- Rarely: an inherited metabolic disease such as MCADD, which in the Netherlands is screened for through the heel prick and is almost always found in infancy
Result
What does the result mean?
Acylcarnitine too high
A raised acylcarnitine means that relatively much carnitine is bound to fatty acid or amino acid residues. This is most often caused by prolonged fasting, being ill, a low-carbohydrate or ketogenic diet or heavy exercise: the body then burns a lot of fat. Reduced kidney function and certain medicines, such as valproic acid, also raise the value. A strongly raised pattern of one particular type may point to an inherited disorder of fatty acid breakdown; in adults this is rare and then usually already known.
Acylcarnitine too low
A low value means that little carnitine is bound, and is the usual result in someone who has eaten well. A low value causes no symptoms and has no separate meaning. With a low total carnitine, for example due to dialysis or low intake, acylcarnitine can also be low; then mainly total carnitine is meaningful.
After an abnormal result
With a raised value, the GP first looks at the circumstances of the sample collection, such as fasting, illness, exercise and diet, and at kidney function and medicines. If the value remains raised without explanation, or if there are symptoms of the muscles, heart or low blood sugar during fasting, referral follows to an internist (specialist in internal medicine) or a specialized center for metabolic diseases.
Reliability
How reliable is the test?
A single total acylcarnitine value can hardly be interpreted. What does give information is the profile of the individual acylcarnitines, assessed together with free and total carnitine and with the circumstances of the sample collection. There are no agreed cut-off values for a total value. Inherited disorders of fatty acid breakdown are screened for in the Netherlands with the heel prick in newborns; an abnormal value in an adult almost never points to one.
What can affect the result?
- Fasting, being ill, heavy exercise and a low-carbohydrate or ketogenic diet raise the value sharply; how long someone had fasted largely determines the result.
- Reduced kidney function and medicines such as valproic acid raise the value.
- A total value hides the pattern; without the individual types, it is not possible to see which step in fatty acid breakdown is failing.
- Measurement methods and reference values differ per laboratory and are not standardized.
Who it is for
Who is the test useful for?
Useful for
The result is mainly meaningful when a metabolic disease is suspected, as part of a full profile. In adults without symptoms, a single total value cannot be interpreted and an abnormality usually does not change the approach. For newborns, screening takes place through the heel prick.
How common is it?
Inherited disorders of fatty acid breakdown are rare. In the Netherlands, on average 15 to 20 children with MCADD are born each year and about 1 child with CPT1 every five years; both are included in the heel prick. A slightly raised acylcarnitine due to fasting or a low-carbohydrate diet is fairly common in healthy adults.
RIVM, prenatal and neonatal screening (heel prick)
Drawbacks and risks
- A rise due to fasting or a low-carbohydrate diet can wrongly be read as a metabolic disease and lead to unnecessary, burdensome follow-up testing.
- A normal total value does not rule out a disorder of fatty acid breakdown, because the pattern of the individual types is decisive.
Get tested
Acylcarnitine: test panels
Acylcarnitine is part of these test panels. You order online and have your blood drawn at a collection point or collect the sample at home.
Evidence
Sources
This explanation is based on Dutch guidelines and independent information. It is general information, not a diagnosis. Discuss an abnormal result with your GP.
More about risks and resultsMore explanations
Other tests: Vitamins, minerals and amino acids
- AC/FC ratio
- Alanine
- Antibodies against intrinsic factor
- Arginine
- Calcium
- Calcium (albumin-corrected)
- Carnitine, free
- Carnitine, total
- Coenzyme Q10
- Copper
- Folic acid
- Glutamic acid (urine)