C18:1 Oleyl (Octadecenoyl) acylcarnitine

This test measures C18:1 oleylcarnitine, a long‑chain acylcarnitine formed when the fatty acid oleic acid is linked to carnitine. Acylcarnitines help move fatty acids into mitochondria, where they are used to make energy, especially when you are fasting or ill.

It is usually performed as part of an acylcarnitine profile by tandem mass spectrometry on a dried blood spot, serum, or plasma. Your clinician may order it alone or with related markers to better understand how your body is handling long‑chain fats.

C18:1 oleylcarnitine can be higher when there are problems transporting or processing long‑chain fats in mitochondria. This pattern is seen in certain inborn errors of metabolism, such as carnitine palmitoyltransferase II deficiency or carnitine‑acylcarnitine translocase deficiency, and may also shift during serious illness, prolonged fasting, or muscle injury. In newborns, it helps evaluate abnormal screening results or symptoms such as poor feeding, lethargy, or low blood sugar.

Your provider may use this result to decide if more metabolic testing is needed, to monitor a known fatty acid oxidation disorder, or to assess risk during periods of stress. Interpreting C18:1 together with other acylcarnitines and your clinical story improves accuracy and helps guide care.

Your result is interpreted in the context of age‑specific reference intervals, the collection conditions, and other acylcarnitine findings. A value above the expected range does not by itself diagnose a disease. Transient changes can occur with fasting, fever, hard exercise, or certain diets and supplements. Patterns that include other long‑chain acylcarnitines and specific ratios are often more informative than a single value.

If your value is higher than expected, your clinician may repeat testing when you are well fed, review medications and supplements, and order follow‑up studies such as a full acylcarnitine profile, free carnitine, urine organic acids, or genetic testing. If your value is within the expected range, that is generally reassuring, but your provider will still consider symptoms and other labs. Always discuss results with your care team to decide on next steps.