Platform
Company
Immunology & Autoimmune
Review status
Currently under review
Pending specialist review and validation.
This test measures the ratio of two acylcarnitines in your blood: glutarylcarnitine (C5DC) and palmitoylcarnitine (C16). It is typically performed by tandem mass spectrometry, often on a dried blood spot. The result is a unitless ratio that helps normalize for overall carnitine levels.
Glutarylcarnitine is a marker that can increase in glutaric acidemia type I (GA1), a rare inherited condition caused by reduced activity of the enzyme glutaryl‑CoA dehydrogenase. The C5DC/C16 ratio is used in newborn screening and in follow‑up metabolic evaluations to improve detection of GA1 and to help decide if more testing is needed.
Finding GA1 early can help prevent serious neurologic injury. The C5DC/C16 ratio is used to flag people who may have GA1 so that confirmatory tests and treatment can begin promptly. If GA1 is confirmed, care usually includes a specialized diet, carnitine supplementation, and careful management during illnesses to reduce the risk of metabolic crises.
Your clinician may order this test after an abnormal newborn screen, if there is a family history of GA1, or if symptoms suggest a metabolic disorder. It is also used alongside other acylcarnitine markers and urine organic acids to build a clearer picture of your metabolic status.
A higher‑than‑expected C5DC/C16 ratio suggests possible GA1, but the ratio alone does not make a diagnosis. Your clinician will consider your symptoms, medical history, and other laboratory tests. Follow‑up often includes urine organic acids, plasma acylcarnitines, and genetic testing of the GCDH gene to confirm or rule out GA1.
Results can be influenced by age, nutrition, carnitine status, and recent illness. Some people with GA1 can have results that vary over time, especially after treatment has started. If your result is unexpected, your clinician may repeat the test or use additional testing to clarify the cause and guide 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.
Newborn values can shift in the first days of life, and fevers or intercurrent illness can alter acylcarnitine patterns. Collecting the sample when stable, or repeating it later, may improve interpretability.
Taking carnitine supplements, total parenteral nutrition, or having low carnitine stores can change acylcarnitine ratios. Let your care team know about supplements and nutrition support.
Blood transfusions before sample collection can affect newborn screening results. The test is often done on dried blood spots, but plasma testing may be used in follow‑up and can yield different patterns.
Certain medicines and specialized diets can modify fatty acid and carnitine metabolism. For example, valproate or ketogenic regimens may influence acylcarnitine profiles and should be disclosed.
Preterm or low birth weight infants can have different baseline acylcarnitine levels and carnitine stores, which may lead to false positive or inconclusive screening results.
Improper drying, heat, humidity, or delays in processing dried blood spots can degrade analytes and distort ratios. Laboratories follow strict protocols to minimize these issues.
References