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FLC immunoassays can be used on urine samples as an alternative to urine electrophoretic tests. However, urinary FLC immunoassays do not solve any of the practical problems of urine collection or overcome the influence of the renal threshold for passage of FLCs into the urine. Indeed, the broad normal range for the κ/λ FLC ratio in urine (Section 6.4) ensures that uIFE is usually more sensitive for the detection of monoclonal FLC. For this reason, international guidelines do not recommend the measurement of urine FLC levels (Chapter 25) [136]. This is further discussed in Chapter 24, which brings together all the arguments for the use of serum rather than urine for the measurement of FLCs.