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. Use in medicine In diabetes, maintaining a normal blood glucose is essential to preventing many medical complications, including heart attacks, diabetic nephropathy, diabetic neuropathy and also diabetic retinopathy eventually leading to blindness. Most commonly, blood sugars are measured by either blood glucose monitoring which measures the current blood glucose level, or by glycated hemoglobin (HbA1c) which measures average glucose levels over approximately 3 months. In a similar way to hemoglobin A1c testing (which measures the glycation of hemoglobin), fructosamine testing determines the fraction of total serum proteins that have undergone glycation (the glycated serum proteins). Since albumin is the most abundant protein in blood, fructosamine levels typically reflect albumin glycation. (Some fructosamine tests specifically quantify the glycation of albumin, or glycated serum albumin instead of all proteins.). Because albumin has a half-life of approximately 20 days, the plasma fructosamine concentration reflects relatively recent (1–2 week) changes in blood glucose. In patients with diseases that reduce red blood cell lifespan, such as hemolytic anaemia or hemoglobinopathies such as sickle-cell disease, a hemoglobin-based A1c test can be misleadingly low. A1c results may also be falsely high or low in hemoglobinopathies because abnormal hemoglobin variants can interfere in the analysis. In these cases, fructosamine measurement can be used as a marker of blood sugar levels, as its measurements are based on albumin instead of hemoglobin. However, any condition that changes serum albumin (such as the nephrotic syndrome) will affect the fructosamine result. In practice, fructosamine is rarely measured clinically (even in individuals with hemoglobinopathies or other red cell disorders) due to a number of pragmatic