Simple assay of serum copper fractions by ultrafiltration and flameless atomic absorption

The authors present a simple and rapid method for assaying ultrafilterable copper (Cu UF) and albumin-bound copper (Cu ALB). It is based on the ultrafiltration of serum in the presence of ethylenediaminetetraacetic acid (EDTA), used to prevent adsorption on the membranes. EDTA at 0.4 g/L has no effect on the equilibrium of serum copper vectors and enables Cu UF to be assayed by flameless atomic absorption. EDTA at 2 g/L is used to assay total exchangeable copper (CU EXC) (ultrafilterable + albumin-bound). The evaluation criteria of the method are furnished, as are the normal values in healthy subjects: 14.6 micrograms/L for Cu UF and 87 micrograms/L for Cu EXC. Finally, the usefulness of the methods described here for the diagnosis of Wilson's and Menkes' disease was demonstrated.