Platform
Company
Immunology & Autoimmune
Review status
Currently under review
Pending specialist review and validation.
This test reports the ratio of two long-chain acylcarnitines, palmitoylcarnitine (C16) and oleoylcarnitine (C18:1), summed together and compared with acetylcarnitine (C2). It is derived from an acylcarnitine profile measured by tandem mass spectrometry on blood, and it reflects how your body moves long-chain fats into mitochondria for energy.
An out-of-pattern result can point to problems using long-chain fats for energy, which may occur in conditions such as carnitine palmitoyltransferase II deficiency or carnitine-acylcarnitine translocase defects. Clinicians may order this ratio as part of follow-up after an abnormal newborn screen, during evaluation of exercise-induced muscle pain or dark urine, or when there are episodes of low blood sugar with poor ketone production.
Your result is interpreted together with the full acylcarnitine profile, your symptoms, and other labs. A higher ratio can be a clue to reduced transport or processing of long-chain fats, while a typical ratio makes these disorders less likely.
Many non-genetic factors can influence the ratio, so a single result rarely provides a final diagnosis. If your value is unexpected, your clinician may repeat testing when you are well, review diet and medications, and consider enzyme or genetic testing.
Prompt follow-up is especially important for infants and for anyone with muscle symptoms or episodes of low energy.
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.
Recent fasting, fever, or infections can shift acylcarnitine patterns and alter this ratio by increasing reliance on fat oxidation. When possible, testing is best performed when you are clinically stable.
Dried blood spot and plasma can differ slightly, and samples taken during or right after a metabolic crisis may look different from baseline. Let your clinician know when the sample was collected relative to symptoms.
Valproic acid, pivalate-containing antibiotics, and high-dose carnitine or medium-chain triglyceride oils can modify acylcarnitine profiles and affect this ratio. Provide a complete medication and supplement list.
Very high-fat diets, ketogenic diets, or prolonged low-calorie intake can change acylcarnitine ratios by altering fuel use. Consistent intake before testing helps with interpretation.
Newborns, premature infants, and pregnant individuals can have physiologic shifts in acylcarnitines. Reference interpretation and follow-up strategies may differ in these groups.
Intense exercise, muscle injury, or rhabdomyolysis can elevate long-chain acylcarnitines and influence the ratio. Avoid strenuous activity just before testing if advised by your clinician.
References