Occasional sample non-linearity (i.e. when a sample measured at different dilutions gives a substantially different result) occurs with most immunoassays. Examples of sample non-linearity with Freelite assays are described and discussed in Section 7.4. Pretorius et al.  reported that sample non-linearity occurred in approximately half of all monoclonal and polyclonal samples, with both Freelite and N Latex FLC assays. The authors concluded that non-linearity of FLC assays is a property of the individual sample and not a method-specific phenomenon. Freelite assays undergo validation during development (based on protocols defined by the Clinical and Laboratory Standards Institute) to ensure that the assays are linear (Section 5.6).