Glycated lysine increases in serum samples stored at -20°C

Abstract

The glycated lysine in serum protein was determined by HPLC measurement of furosine in hydrolyzed serum, with synthetic N(α)-Boc-N(ε)-(1-deoxy-D-fructosyl)-L-lysine as the standard. The glycated lysine value increased with time of storage when the serum was kept at -20°C, possibly because of an ongoing reaction between glucose and the ε-amino groups of lysine in the frozen serum. The problem was eliminated by using storage at -70°C or by acidifying the serum before storing it at -20°C.