C8/C10 MCAD ratio

The C8/C10 MCAD test measures the ratio of two medium-chain acylcarnitines in your blood, octanoylcarnitine (C8) and decanoylcarnitine (C10). These molecules reflect how your cells break down certain fats for energy through the fatty acid oxidation pathway.

It is typically performed as part of a comprehensive acylcarnitine profile by tandem mass spectrometry, using a small blood sample from a vein or a dried blood spot. Clinicians use this ratio to help evaluate for medium-chain acyl-CoA dehydrogenase deficiency, a genetic condition that affects energy production, especially during fasting or illness.

An abnormal C8/C10 ratio can suggest a problem with the enzyme that processes medium-chain fats, which may lead to low blood sugar, lethargy, seizures, or liver stress during periods without food or during infections. Identifying this pattern early allows steps to prevent metabolic crises and to guide safe nutrition and sick-day plans.

Your clinician may order this test as follow-up to newborn screening, to investigate symptoms like vomiting after fasting, poor tolerance to illness, or unexplained episodes of low energy, or when there is a family history. It can also support monitoring in people with a known diagnosis.

Your result is interpreted together with your symptoms, exam findings, and other laboratory tests, such as the absolute C8 level, a full acylcarnitine profile, and urine organic acids. Genetic testing of the ACADM gene may be recommended if the pattern suggests medium-chain acyl-CoA dehydrogenase deficiency.

If your ratio is outside the expected range, your healthcare professional may repeat testing when you are well, check carnitine status, and refer you to a metabolic specialist. Most people who are identified and follow dietary and illness management plans do well. Do not change feeding or fasting practices without medical guidance.