Retrospective study of quantitative free light chain levels in random urine of patients with multiple myeloma

Abstract

The traditional method to quantify the immunoglobulin free light chains (FLCs) in patients with multiple myeloma (MM)is based on either their serum levels or on 24-hour urine collections. The latter method is cumbersome and ofteninaccurate, and serum levels are currently the preferred method for quantifying FLCs in MM. Scarce data exist on the FLCquantification in random urine samples. In this study, we first compared serum and urine levels of FLCs measured in24-hour specimens obtained from 56 consecutive MM patients. We subsequently examined the same correlation in 209random urine specimens obtained from a second cohort of 117 consecutive MM patients. Serum FLCs were highlycorrelated, both with the 24-hour and the random urine specimens. With the latter, the Pearson coefficient r was 0.805 and0.748 for kappa and lambda light chains, respectively (p<0.001), even in the presence of renal insufficiency. Random urineFLCs levels >1.2 mg/dL predicted a positive urine immunofixation with a specificity and sensitivity of 52.7% and 95.8%,respectively. Since random urine quantification of kappa and lambda FLCs paralleled their serum counterparts over time,this method could represent an additional non-invasive test for assessing disease activity in MM patients.