Many allergens are glycoproteins i.e., they contain one or several complex oligosaccharide chains linked to the peptide structure of the protein. Since glycoepitopes can share significant structural homologies beyond the limits of protein families, they are prone to cause extensive antibody cross-reactivity. A number of these epitopes have thus been designated Cross-reactive Carbohydrate Determinants or CCDs.
A CCD test could be useful when in-vitro results do not match the clinical picture (e.g. symptoms, skin tests, etc.), especially when numerous positive results to natural extract allergens are found without obvious clinical symptoms to all of them.