2-Methylbutyryl-L-carnitine-d3 is intended for use as an internal standard for the quantification of 2-methylbutyryl-L-carnitine by GC- or LC-MS. 2-Methylbutyryl-carnitine is a naturally occurring acylcarnitine that is produced via L-isoleucine metabolism.{42603} Plasma levels of 2-methylbutyryl-carnitine are elevated in patients with non-alcoholic steatohepatitis (NASH).{42604} Elevated levels of 2-methylbutyryl-carnitine are associated with 2-methylbutyryl-CoA dehydrogenase deficiency (2-MBCDD), also known as short/branched chain acyl-CoA dehydrogenase (SBCAD) deficiency.{42605}