Evaluation of latex-enhanced nephelometric reagents for measuring free

Evaluation of latex-enhanced nephelometric reagents for measuring free immunoglobulin light-chains on the Radim Delta P. J. 1 The 1, Showell E. A. 1, Lynch H. D. 1, Carr-Smith A. R. 2 Bradwell Binding Site Ltd. , PO Box 11712, Birmingham, B 29 6 AT, UK, 2 Division of Immunity and Infection, The Medical School, University of Birmingham, B 15 2 TT, UK (Presented at AACC 2004, Los Angeles, USA. 2004 (Clin Chem 2004, 50, No. 6 Supplement C-40, p. A 81) Introduction The instrument was programmed to construct a calibration curve from dilutions of a single calibration fluid. The standard curves were validated by assay of control fluids. Samples were initially measured at the standard programmed sample dilution and if out of range the instrument automatically re-measured the sample at appropriate alternative dilutions. All dilutions were made with the instrument’s on-board pipetting system, which was able to make dilutions between neat and 1/2000. The main assay characteristics are summarized in the table below. The assays were found to be linear over their measuring ranges for both kappa and lambda assays (Figure 1). Kappa Free Linearity Lambda Free Linearity 180 y = 0. 9981 x - 0. 2097 Results R = 0. 9999 140 120 100 80 60 40 20 20 0 50 100 150 200 0 50 100 150 Calculated results (mg/L) 200 Figure 1: The assay linearity of The Binding Site FLC assays for use on the Radim Delta. Good agreement was observed when these assays were compared with The Binding Site FLC assays for the Dade. Behring BN™II (Figure 2). Kappa Free Comparison Table 2: Intra- and inter-assay precision at three antigen concentrations for The Binding Site FLC assays on the Radim Delta. 1400 y = 0. 9487 x + 2. 8621 r = 0. 986 1200 1000 800 600 400 200 0 Table 1: The assay parameters of The Binding Site FLC assays for use on the Radim Delta. Lambda Free Comparison 3000 0 Trademarks: BN™II is a registered trademark of Dade Behring Gmb. H, Marburg, Gmb. H 120 Calculated results (mg/L) Interference was within ± 4% when haemoglobin, bilirubin or chyle were added to serum samples of known free light chain concentrations (Table 3). Intra- and inter-assay precision were assessed at three antigen levels for both assays. The assay linearity was calculated by assaying serially diluted serum samples over an antigen concentration range of 0. 5 – 168 mg/L for Kappa free and 6. 6 – 170 mg/L for Lambda free, and comparing with expected results. R 2 = 0. 9992 140 40 Assay imprecision expressed as % coefficient of variation was from 2. 0 – 7. 7% for within-run and 5. 02 – 9. 0% for between-run studies (Table 2). y = 1. 0032 x - 1. 1933 160 2 Observed results (mg/L) 160 Lambda Free Radim Delta (mg/L) Method The assay was tested for possible interference from coexisting substances by adding haemoglobin (3 g/L), bilirubin (200 mg/L) and triglyceride (Intralipid; 0. 5%) to serum samples and comparing to an equivalent sample blank. Comparison was made with The Binding Site FLC assays for the Dade Behring BN™II by measuring serum samples from normal subjects, patients with systemic lupus erythematosus and multiple myeloma on both systems and carrying out regression analysis. Kappa Free Radim Delta (mg/L) Assays specific for serum immunoglobulin free light chains (FLC) that are compatible with commonly used laboratory nephelometric and turbidimetric analysers have recently become available. Studies with these assays have shown that serum FLC measurement is useful for the diagnosis and monitoring of patients with primary amyloidosis, non-secretory myeloma and light chain myeloma. Here we describe development of serum FLC assays for use on the Radim Delta, a medium-sized, fully automated bench-top nephelometer. 500 1000 Kappa Free BNII (mg/L) 1500 y = 0. 918 x + 22. 885 r = 0. 99 2500 2000 1500 1000 500 0 0 1000 2000 3000 Lambda Free BNII (mg/L) Figure 2: Comparison of results for The Binding Site FLC assays on the Radim Delta with existing Binding Site FLC assays for use on the Dade. Behring BN™II. Table 3: The interference test results for The Binding Site FLC assays for use on the Radim Delta. The percentage differences between samples diluted with saline and with the potentially interfering substances are shown. Conclusion The assays for the Radim Delta provide a rapid and precise method of measuring FLC in serum and show good agreement with existing assays.