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Chapter 7

All Freelite sFLC assays are validated for the quantification of κ or λ FLCs in serum. In addition, Freelite assays are also available for the measurement of FLCs in urine (Section 4.5.3) or cerebrospinal fluid (Chapter 36).

In general, samples that are haemolysed, lipaemic, or with highly elevated bilirubin should be avoided. The maximum concentration of interfering substance that can be reliably assessed is stated in the product insert. An example of interference testing of κ and λ sFLC assays is shown for the Binding Site SPAPLUS® in Table 7.1.
Interfering substance
Concentration Deviation from target value
κ sFLC λ sFLCs
Haemoglobin 3 g/L 2.1% -1.6%
Intralipid 0.3% -9.1% -3.0%
Bilirubin 300 mg/L -5.0% -2.4%

Table 7.1. Freelite assay interference for κ and λ Freelite assays on the Binding Site SPAPLUS. Interference was tested using a control serum containing ≤10 mg/L sFLCs, tested at the minimum sample dilution (1/1).