OH-Butyrylcarnitine (C4OH), also known as hydroxybutyrylcarnitine, is part of the acylcarnitine family measured to assess mitochondrial and metabolic health. It forms during the metabolism of short-chain fatty acids—especially 3-hydroxybutyrate—and during the breakdown of certain amino acids such as threonine. C4OH serves as a carrier molecule that transports hydroxy-acyl groups into and out of mitochondria, allowing cells to regulate energy production and maintain metabolic balance.
Levels of C4OH can shift with changes in energy demand, fasting status, diet composition, and mitochondrial efficiency. Because it sits at the intersection of fatty acid oxidation and ketone body metabolism, C4OH is particularly informative when evaluating metabolic flexibility, ketosis, or mitochondrial stress. While rare, abnormalities in C4OH may also be seen in certain inherited metabolic conditions that affect short-chain or hydroxy-acyl metabolism.
When interpreted alongside other acylcarnitines—especially C4, C3, and ketone-related markers—C4OH helps provide a clearer picture of how the body is generating, transporting, and burning fuel.
OH-Butyrylcarnitine, C4OH
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