Freelite immunoassays are available for a range of nephelometric and turbidimetric laboratory instruments, including the Binding Site SPAPLUS® and Optilite® instruments (Chapter 37). Between-platform agreement of sFLC results is good (Section 5.8). Factors that may influence a laboratory’s choice of instrument include features of the sFLC assays on a particular platform (assay time, prozone parameters etc.), as well as those related to general laboratory organisation (workload, complete testing menu offered, existing platforms already present etc.). It is recommended that all laboratories performing sFLC assays participate in external quality assurance (EQA) schemes. These are further discussed in Chapter 38.