Glomerular filtration rate as a determinant of free light chains in renal transplantation.

BACKGROUND

Transplant patients have an increased incidence of lymphoproliferative disorders. The development of a sensitive immunoassay for serum free light chain (sFLC) determination has improved the diagnosis of monoclonal gammapathy. However, metabolism of FLC largely depends on renal function which could lead to misinterpretation of results. The aim of this study was to assess polyclonal FLC in kidney transplant recipients in relation to markers of renal function.

MATERIALS AND METHODS

97 renal transplant patients (median transplantation follow-up of 2.2 years) were included in this study. Kappa FLC, lambda FLC and cystatin C were measured by particle-enhanced turbidimetric immunoassay (PETIA) using kits from a Binding Site (Birmingham, UK) SPAPLUS(®) analyzer. Glomerular filtration rate was measured using urinary clearance of (99m)Tc-DTPA and estimated using CKD-EPI creatinine 2009, CKD-EPI cystatin C 2012 and CKD-EPI creatinine-cystatin C 2012.

RESULTS

Serum kappa FLC was 22.38 [6.39-68.91] mg/L and serum lambda FLC was 15.66 [7.29-50.81] mg/L. Both levels of kappa and lambda were correlated with renal function. Median κ/λ ratio was 1.34 [0.57 to 2.67] leaving 19.6% of renal transplant patients outside the normal reference range [0.26-1.65]. However, using a reference interval normalized by renal function [0.37-3.1], none of our patients was classified as abnormal.

CONCLUSION

κ/λ ratio should be cautiously analyzed in renal transplantation and renal function, estimated by creatinine/cystatin C equations should be taken into account.