Platform
Company
Complement
Review status
Currently under review
Pending specialist review and validation.
This test measures the ratio between two acylcarnitines in your blood: C3 (propionylcarnitine) and C16 (palmitoylcarnitine). Acylcarnitines are small molecules that form when your body breaks down fats and certain amino acids, and they are commonly assessed using tandem mass spectrometry.
The C3/C16 ratio helps show the balance between short‑chain and long‑chain acylcarnitines. Doctors use it alongside a full acylcarnitine profile to better understand how your metabolism is functioning and whether there might be an inherited or acquired issue with specific metabolic pathways.
An abnormal C3/C16 ratio can be a clue to conditions that affect how your body processes certain nutrients, such as disorders involving propionyl‑CoA metabolism or issues with long‑chain fatty acid handling. It is often used with other markers to evaluate for conditions like propionic acidemia, methylmalonic acidemia, nutritional vitamin B12 deficiency, or fatty acid oxidation problems.
Your clinician may order this test if you or your child has symptoms such as poor feeding, vomiting, low energy, unexplained illness, or if a newborn screening suggested a possible metabolic condition. It can also support monitoring during treatment or when dietary or vitamin therapy is being adjusted.
Your result is interpreted in the context of your overall acylcarnitine profile, medical history, diet, and any symptoms. A higher ratio may suggest an increase in propionylcarnitine relative to palmitoylcarnitine, but this pattern alone does not confirm a diagnosis. A lower ratio can be seen in other physiologic states or with certain therapies. The result is a piece of a larger puzzle and is best understood alongside other laboratory tests.
If your result is outside the expected range, your clinician may repeat testing, review your diet and supplements, and order additional studies such as plasma amino acids, urine organic acids, vitamin B12 and related markers. Prompt follow‑up helps distinguish temporary or nutritional causes from inherited metabolic conditions, and guides safe, practical next steps.
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.
Fasting, poor intake, or acute illness can shift acylcarnitine patterns and change the C3/C16 ratio. Let your clinician know if you were sick or had not eaten normally when the sample was collected.
Carnitine supplements, certain antibiotics, and medicines that affect liver or mitochondrial function can alter acylcarnitines. Provide a complete list of all vitamins, herbal products, and prescriptions.
Low vitamin B12 can raise propionylcarnitine and influence the ratio. Recent B12 injections or high oral doses may temporarily normalize results, so timing and clinical context matter.
Results can differ between plasma and dried blood spot testing, and with delays in processing or improper storage. Accurate collection and prompt handling reduce pre‑analytic variability.
Newborns, premature infants, pregnant individuals, and people with kidney or liver disease can have different acylcarnitine patterns. Interpretation should account for these factors.
High protein intake, specialized formulas, or parenteral nutrition can affect acylcarnitines. Share details about recent diet, including medical foods or ketogenic therapy.
References