Platform
Company
Immunology & Autoimmune
Review status
Currently under review
Pending specialist review and validation.
This test measures the ratio of C18-hydroxyacylcarnitine (C18-OH) to stearoylcarnitine (C18) in a blood sample using tandem mass spectrometry. It reflects how your body breaks down long-chain fats inside the mitochondria. The ratio serves as a biochemical marker of the activity of long-chain 3-hydroxyacyl-CoA dehydrogenase, an enzyme that is part of the mitochondrial trifunctional protein.
Clinicians use this ratio to evaluate for long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency, often called LCHAD deficiency, and related trifunctional protein disorders. It is commonly performed as part of an acylcarnitine profile in follow-up to newborn screening, in people with suggestive symptoms, or for monitoring known fatty acid oxidation conditions.
If LCHAD activity is reduced, certain fatty acid byproducts can accumulate during fasting, illness, or prolonged exercise. This can lead to low blood sugar without ketones, muscle breakdown, heart or liver problems, and episodes of weakness or lethargy. Identifying an abnormal pattern early helps prevent serious complications through dietary management and prompt care during stress or illness.
Your clinician may order this test after an abnormal newborn screen, when symptoms suggest a fatty acid oxidation disorder, or if there is a family history. It can also help monitor response to therapy, including specialized diets and medium-chain triglyceride supplementation, and guide plans for sick-day management.
A higher ratio can suggest decreased LCHAD activity, but interpretation always occurs in context. Your care team may confirm findings with a full acylcarnitine profile, urine organic acids, genetic testing of the HADHA and HADHB genes, and sometimes enzyme studies. Diet, supplements, intercurrent illness, and the timing of collection are considered before conclusions are made.
If your result is unexpected, your clinician might repeat testing when you are well or after specific preparation to reduce confounding. Do not change your diet or medications on your own. Seek urgent medical attention if you develop concerning symptoms such as vomiting, unusual sleepiness, or muscle pain, and follow your emergency plan if one has been provided.
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.
Being ill, fasting, or having poor intake before collection can shift acylcarnitine patterns and may raise long-chain hydroxyacylcarnitines. Follow your lab’s preparation instructions and tell your clinician if you were sick at the time of sampling.
Dried blood spots that are old, heat exposed, or humidified can degrade analytes and distort ratios. Prompt drying, proper storage, and timely analysis improve accuracy.
Medium-chain triglyceride formulas can lower certain long-chain acylcarnitines, while carnitine supplements can alter the overall profile. Share details about special diets, formulas, and supplements with your care team.
Some drugs, such as valproate or high-dose salicylates, can affect mitochondrial fat oxidation and acylcarnitine profiles. Provide a complete list of prescription and over-the-counter medicines.
Intense exercise shortly before testing can transiently change muscle metabolism and acylcarnitine levels. Avoid unusual exertion prior to collection unless your clinician advises otherwise.
Newborn physiology and pregnancy can influence results. Mothers carrying an affected fetus can develop liver complications; clinicians consider maternal and fetal context when interpreting this marker.
References