Platform
Company
Immunology & Autoimmune
Review status
Currently under review
Pending specialist review and validation.
This test measures stearoylcarnitine, also called octadecanoylcarnitine or C18, in your blood. Stearoylcarnitine is a long‑chain acylcarnitine formed when the body links carnitine to a long‑chain fatty acid. It is part of the acylcarnitine profile commonly performed by tandem mass spectrometry.
Results help show how well your cells transport long‑chain fatty acids into mitochondria and break them down for energy. The test may be done on a dried blood spot in newborn screening or on plasma or serum in diagnostic evaluations across all ages.
Abnormal C18 levels can point to problems with long‑chain fatty acid oxidation or carnitine transport. Elevated values may be seen in conditions such as carnitine palmitoyltransferase II deficiency or carnitine‑acylcarnitine translocase deficiency, and can also be influenced by nutritional status, liver function, or certain medications. This marker is often reviewed together with other acylcarnitines and clinical findings.
Clinicians order this test when a newborn screen flags a possible fatty acid oxidation disorder, or when children or adults have unexplained low energy, muscle breakdown, heart concerns, or hypoglycemia during illness or fasting. Timely interpretation can guide follow‑up testing, dietary changes, and emergency plans to prevent complications.
Your result is interpreted in context with age, symptoms, and the pattern of other acylcarnitines. A higher result does not by itself diagnose a disease. If your value is outside the expected range, your clinician may repeat the test, review a full acylcarnitine profile, check free and total carnitine, and consider enzyme activity or genetic testing to confirm or rule out a fatty acid oxidation disorder.
A result within the expected range is generally reassuring, but does not exclude all metabolic conditions. If you or your child had symptoms when the sample was collected, your clinician may still recommend follow‑up. Never change diet or supplements without discussing the result and next steps with your care team.
Reference intervals vary by laboratory, analyzer, methodology, population, and units. The ranges shown here are for education only. Always interpret your results against the reference interval printed on your own lab report.
Prolonged fasting, fever, or acute illness can shift fatty acid use and raise long‑chain acylcarnitines, including C18. Let your clinician know your fasting status and recent illnesses when the sample was taken.
Prescription or over‑the‑counter carnitine can alter acylcarnitine patterns. Share any carnitine doses, nutritional shakes, or metabolic formulas you are taking before testing.
Drugs such as valproate and some antibiotics, as well as total parenteral nutrition or lipid emulsions, may affect acylcarnitine levels. Provide a complete medication and infusion history.
Dried blood spots collected too early after birth, hemolyzed plasma, or delayed processing can shift results. Repeat testing or plasma confirmation may be needed if the first sample was suboptimal.
In newborns, maternal carnitine status, prematurity, and recent transfusions can influence acylcarnitine patterns. Clinicians often review maternal history and may test the mother if needed.
Impaired liver or renal function can change fatty acid handling and carnitine balance, which may modify C18 concentrations. Relevant chemistry tests help with interpretation.
References