Glycated hemoglobin (glycohemoglobin, HbA1c, hemoglobin A1c, A1c, or less commonly HbA1c, HgbA1c, Hb1c, etc.) is a form of hemoglobin (Hb) that is chemically linked to a sugar. Most monosaccharides, including glucose, galactose and fructose, spontaneously (i.e. non-enzymatically) bond with hemoglobin, when present in the bloodstream of humans. However, glucose is less likely to do so than galactose and fructose (13% that of fructose and 21% that of galactose), which may explain why glucose is used as the primary metabolic fuel in humans.