Abstract: The present invention relates to a method for quantifying a non-proteinaceous corn pound bound to one or more carrier proteins in a sample comprising the steps of: i) separating complexes of said non-proteinaceous compound bound to said one or more carrier proteins from the non-proteinaceous compound that is not bound to said one or more carrier proteins; ii) releasing the non-proteinaceous compound from said one or more carrier proteins by treating the complexes of (i) with one or more enzymes; and iii) quantifying the non-proteinaceous compound enzymatically released in step (ii). In a preferred embodiment, the non-proteinaceous compound is cobalamin or an analogue thereof, and the carrier protein is transcobalamin or haptocorrin. The invention further relates to a method for quantifying a glycoprotein in a sample comprising the steps of: i) treating a sample with deglycosylating enzyme; and quantifying said glycoprotein. In a preferred embodiment, said glycoprotein is haptocorrin.