Fasting serum and 24-hour urine were taken from each patient in the same period. The following tests were performed: serum FLC κ, serum FLC λ, SCr, serum β2-microglobulin, urinary FLC κ, urinary FLC λ, urinary α1-microglobulin, and urinary β2-microglobulin. Serum levels of creatinine were determined by an enzymatic method (Hitachi 008AS Automatic biochemical analyzer, Tokyo, Japan). Other items were tested by Siemens BN II. FLC in serum and urine were detected by the Freelite™ assay (IMMAGE 800, the Binding Site Ltd, Birmingham, UK) and the N-Latex FLC assay (Siemens BN II, Siemens, Germany) at the same time.
We chose to use the reference ranges proposed in the literature [5 (link), 6 (link), 9 (link)]: N-Latex: FLC κ6.7-22.4 mg/L; FLC λ 8.3-27.0 mg/L, FLC κ/λ0.31-1.56; Freelite: FLC κ 3.3.0-19.40 mg/L; FLC λ 5.71-26.30 mg/L, FLC κ/λ 0.26-1.65 (0.37-3.10 mg/L if eGFR < 60 mL/min/1.73 m2).
We chose to use the reference ranges proposed in the literature [5 (link), 6 (link), 9 (link)]: N-Latex: FLC κ6.7-22.4 mg/L; FLC λ 8.3-27.0 mg/L, FLC κ/λ0.31-1.56; Freelite: FLC κ 3.3.0-19.40 mg/L; FLC λ 5.71-26.30 mg/L, FLC κ/λ 0.26-1.65 (0.37-3.10 mg/L if eGFR < 60 mL/min/1.73 m2).