3-Hydroxyisovalerylcarnitine is a carnitine derivative. 3-Hydroxyisovaleryl carnitine in plasma may serve as a novel biomarker of biotin deficiency in humans, with its concentration increasing with biotin deficiency. Biotin deficiency reduces the activity of biotin-dependent 3-methylcrotonyl-CoA carboxylase, hinders the conversion of 3-methylcrotonyl-CoA into 3-methylglutaconyl-CoA, and impairs the leucine catabolism pathway; resulting in plasma 3-Hydroxyisovalerylcarnitine concentrations rise^[1].