Platform
Company
Immunology & Autoimmune
Review status
Currently under review
Pending specialist review and validation.
This test measures the ratio of hydroxy-palmitoylcarnitine (C16-OH) to palmitoylcarnitine (C16) in blood. These molecules are acylcarnitines, which are byproducts formed as the body breaks down long-chain fats for energy. The ratio reflects how well a specific step of fat oxidation is working in your cells.
It is most often used as a marker for long-chain 3-hydroxyacyl-CoA dehydrogenase activity, a component of the mitochondrial trifunctional protein. The test is typically performed by tandem mass spectrometry and is commonly included in acylcarnitine profiles, newborn screening follow-up, or confirmatory metabolic evaluations.
Clinicians use this ratio to help evaluate for long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency or related mitochondrial trifunctional protein disorders. These conditions can lead to problems using fat for energy, especially during illness or fasting, and may cause low blood sugar, muscle breakdown, heart or liver issues, and in some cases nerve or eye complications.
Your provider may order this test if there is an abnormal newborn screen, a history of unexplained hypoglycemia, recurrent rhabdomyolysis, cardiomyopathy, or liver dysfunction, or to help assess similar symptoms in a family member. Identifying an issue early supports nutrition-based management, avoidance of prolonged fasting, and planning for sick-day care to reduce complications.
A higher C16-OH/C16 ratio can suggest reduced activity of the long-chain 3-hydroxyacyl-CoA dehydrogenase step, which is seen in long-chain fatty acid oxidation disorders such as LCHAD or mitochondrial trifunctional protein deficiency. However, temporary changes can occur during acute illness, with certain supplements or medications, or in premature infants, so results are interpreted in context with your health status and other lab findings.
If your result is outside the expected range, your clinician may repeat testing when you are well, review a full acylcarnitine profile, check related labs, and consider genetic testing of the HADHA and HADHB genes or enzyme studies. A metabolic genetics specialist can guide next steps and discuss nutrition strategies and emergency plans. Do not change your diet or medications without medical advice.
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 an acute infection can shift fat metabolism and temporarily raise hydroxyacylcarnitines, potentially affecting the ratio. When possible, testing during a stable health period gives a clearer picture.
Premature or very young infants can have immature fat oxidation and variable carnitine stores, which may alter acylcarnitine patterns. Follow-up testing and clinical context are important.
Oral carnitine, medium-chain triglyceride products, or specialized formulas can change acylcarnitine profiles. Tell your clinician about all supplements and nutrition products you use.
Some medicines, such as valproate, and parenteral nutrition can influence fatty acid oxidation or assay signals. Provide a complete medication and nutrition history before testing.
Heavy or unaccustomed exercise before sampling can increase muscle fatty acid turnover and affect acylcarnitines. Avoid intense workouts the day prior unless your clinician advises otherwise.
Results may differ between dried blood spot and plasma, and delays in processing or improper storage can degrade analytes. Proper collection and transport help ensure reliable results.
References