image
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 plasma, urine (Section 4.5.3) or cerebrospinal fluid (CSF, 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 and for the Binding Site Optilite in Table 7.2.
Interfering substance
Concentration Deviation from target value
κ sFLC λ sFLC
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).

Interfering substance
ConcentrationMaximum deviation from target value
κ sFLCλ sFLC
Haemoglobin1.25 g/L7.9%5.7%
Intralipid5 g/L-7.5%-7.3%
Bilirubin200 mg/L-3.2%2.5%
Triglyceride10 g/L6.5%-2.9%

Table 7.2. Freelite assay interference for κ and λ Freelite assays on the Binding Site Optilite. Interference was tested across a range of serum samples, including normal, abnormal and samples close to medical decision points.