An international reference material is not available for FLCs, therefore, N Latex FLC and Seralite-FLC assays were both calibrated against the Freelite assays [920][199]. However, the absolute values returned by the monoclonal and polyclonal antisera-based assays do not compare well. Caponi et al. [1184] suggest that this may be explained by differences in the reactivity of Freelite and N Latex reagents towards FLC monomers and dimers in their respective calibrators. This is discussed further in Section 8.6.1.