CPT1 Ratio (C0/(C16 + C18))

The C0/(C16+C18) CPT1 ratio is a calculation made from an acylcarnitine profile, a test that measures different forms of carnitine in the blood. It compares free carnitine (C0) to two long-chain acylcarnitines (C16 and C18). This ratio reflects the function of carnitine palmitoyltransferase 1, an enzyme that helps move long-chain fatty acids into mitochondria so your body can make energy, especially during fasting or illness.

The ratio is derived using tandem mass spectrometry on a small blood sample, often from a dried blood spot or plasma. It is used in newborn screening in many regions and in diagnostic evaluations when a fatty acid oxidation disorder is suspected, particularly carnitine palmitoyltransferase 1A (CPT1A) deficiency.

This ratio helps identify people who may have CPT1A deficiency, a condition that can lead to low blood sugar without ketones, liver stress, and episodes of lethargy during fasting or common illnesses. Finding an abnormal ratio can prompt timely confirmatory testing and early care plans that reduce the risk of serious complications.

Your clinician may order this test after an abnormal newborn screen, if you or your child has symptoms during fasting or infections, or to clarify the cause of unexplained hypoglycemia or liver dysfunction. Results can also guide genetic testing and nutrition strategies. The test uses a routine blood sample and carries minimal risk.

If your CPT1 ratio is higher than expected, it does not by itself diagnose a disorder. Your healthcare provider will interpret it alongside symptoms, exam findings, diet, supplements, and medications, as well as when the sample was collected. Follow-up may include repeating the acylcarnitine profile when you are well, measuring free and total carnitine, checking liver-related labs, urine studies, and targeted genetic testing for CPT1A.

A result within the expected range makes CPT1A deficiency less likely, but it does not completely rule it out. If symptoms persist, your provider may recommend further evaluation or repeat testing. Regardless of the result, you may receive advice on avoiding prolonged fasting, having a sick-day plan, and optimizing nutrition to support safe energy use.