Hexanoylcarnitine (CAS: 6418-78-6), also known as caproylcarnitine, is an acylcarnitine. Numerous disorders have been described that lead to disturbances in energy production and in intermediary metabolism in the organism which are characterized by the production and excretion of unusual acylcarnitines. A mutation in the gene coding for carnitine-acylcarnitine translocase or the OCTN2 transporter aetiologically causes a carnitine deficiency that results in poor intestinal absorption of dietary L-carnitine, its impaired reabsorption by the kidney and, consequently, in increased urinary loss of L-carnitine. Determination of the qualitative pattern of acylcarnitines can be of diagnostic and therapeutic importance. The betaine structure of carnitine requires special analytical procedures for recording. The ionic nature of L-carnitine causes a high water solubility which decreases with increasing chain length of the ester group in the acylcarnitines. Therefore, the distribution of L-carnitine and acylcarnitines in various organs is defined by their function and their physicochemical properties as well. High-performance liquid chromatography (HPLC) permits screening for free and total carnitine, as well as complete quantitative acylcarnitine determination, including the long-chain acylcarnitine profile , 136(8), 1279-1291., Int J Mass Spectrom. 1999;188:39-52.). Hexanoylcarnitine is a medium-chain acylcarnitine present in the urine of patients with medium-chain acyl-CoA dehydrogenase deficiency. Hexanoylcarnitine is also found to be associated with celiac disease and glutaric aciduria II which are both inborn errors of metabolism.