Very Long-Chain Fatty Acids Panel, Serum or Plasma

What This Test Measures

Very long-chain fatty acids (VLCFAs) are a group of fats with unusually long carbon chains. This panel measures several specific VLCFAs in serum or plasma, including molecules such as hexacosanoic acid (C26:0), and often compares them with shorter-chain fatty acids to calculate ratios. These ratios help laboratories and clinicians interpret whether VLCFA levels are normal or suggestive of a disorder.

Why Your Doctor May Order It

Your healthcare provider may order this test if you or your child has symptoms that suggest a problem with fatty acid processing, such as muscle weakness, changes in walking, behavioral or learning concerns, or nerve-related symptoms. It may also be ordered when there is a family history of an inherited metabolic condition or when newborn screening results need follow-up.

How the Sample Is Collected

The test typically requires a blood draw from a vein, collected into a tube that yields serum or plasma. In most cases no special preparation is needed, but your provider or laboratory will tell you if fasting or timing instructions apply. Tell your care team about any medications or supplements you take, since some may affect results.

What the Results Mean

Results are interpreted by comparing your values with the laboratory's reference ranges and by looking at patterns across the fatty acids measured. Elevated VLCFA levels or abnormal ratios can suggest a disorder of fatty acid processing, but results alone do not confirm a diagnosis. Your provider will interpret them alongside symptoms, family history, and possibly additional genetic or biochemical testing.