Fructosamines are compounds that result from glycation reactions between a sugar (such as fructose or glucose) and a primary amine, followed by isomerization via the Amadori rearrangement. Biologically, fructosamines are recognized by fructosamine-3-kinase, which may trigger the degradation of advanced glycation end-products (though the true clinical significance of this pathway is unclear). Fructosamine can also refer to the specific compound 1-amino-1-deoxy-D-fructose (isoglucosamine), first synthesized by Nobel laureate Hermann Emil Fischer in 1886.

Most commonly, fructosamine refers to a laboratory test for diabetes management that is rarely used in human clinical practice (simple blood glucose monitoring or hemoglobin A1c testing are preferred). In small animal veterinary practice however it is part of the diabetic cat or dog diagnosis and monitoring giving an indication of blood glucose levels over the previous week. Many direct-to-consumer lab testing companies sell fructosamine tests.