Prevalence and clinical significance of abnormal serum kappa/lambda light chain ratio in patients with chronic kidney disease.

INTRODUCTION A range of malignant diseases (both solid organ tumors and hematogenous malignancies) may manifest as proteinuria/nephrotic syndrome. Multiple myeloma (MM) typically involves the kidneys and proteinuria, and chronic kidney disease (CKD) may also be the first manifestation of MM. OBJECTIVES The aim of the study was to evaluate the prevalence and clinical significance of abnormal serum free kappa/lambda light chain ratio in patients referred to a renal center for a diagnostic workup for proteinuria or CKD of an unknown origin (or both). PATIENTS AND METHODS Free light chain tests were performed in 92 consecutive patients (mean age, 63 ±13.9 years; women, 38%; men, 62%) using FreeLite kits. In addition, serum creatinine, calcium, and albumin levels as well as estimated glomerular filtration rate (eGFR) were measured and blood count and proteinuria were assessed. In 39 patients, kidney biopsy was also performed. Nephrotic syndrome was found in 38% of the patients; nonnephrotic proteinuria, in 39.1%; and isolated reduction of eGFR (without proteinuria), in 22.9%. RESULTS MM was confirmed in 5 patients (5.43%; all patients had a highly abnormal kappa/lambda ratio). After the exclusion of the subjects with MM, the abnormal kappa/lambda ratio was found in 37 patients (42.5%); MM was excluded in all patients after careful hematological evaluation, including bone marrow biopsy in 12 cases. The percentage of the abnormal kappa/lambda ratio was high regardless of the proteinuria level, eGFR, or the type of glomerulopathy diagnosed by kidney biopsy. The kappa/ lambda ratio did not correlate with age, proteinuria, or eGFR. CONCLUSIONS Our results suggest that an abnormal kappa/lambda ratio (in most cases higher than normal) is a common and, most likely, nonspecific finding in patients with proteinuria or CKD of an unknown origin (or both).