Bovine insulin differs from human insulin in three amino acid residues and is therefore used as internal standard for human insulin. This Certified Spiking Solution^® of fully-intact bovine insulin protein is suitable for quantification of human insulin in LC-MS/MS insulin testing methods. Insulin is a peptide hormone, composed of 51 amino acids, produced by beta cells of the pancreatic islets. Insulin regulates the metabolism of carbohydrates, fats and protein by promoting the absorption of, especially glucose from the blood into liver, fat and skeletal muscle cells. Insulin levels are routinely measured to evaluate insulin production; diagnose insulin-producing tumors; determine hypoglycemia or to identify insulin resistance.