Urine free light chains as a novel biomarker of acute kidney allograft injury.

BackgroundWe evaluated urine free light chains (FLC) as a potential biomarker for acute kidney allograft injury (AKAI). MethodsUrine and FLC were compared with urine -2 microglobulin (2-M), retinol-binding protein (RBP), kidney injury molecule 1 (KIM-1), neutrophil gelatinase-associated lipocalin (NGAL), and microalbuminuria (MAB) in biopsy-confirmed acute rejection (AR) and acute tubular necrosis (ATN). Healthy volunteers (normal) and transplant recipients with normal allograft function (control) were used as references. ResultsCompared with control or normal group (N=15), urine FLC, MAB, and RBP were higher in ATN (N=29) and AR (N=41) groups (p<0.05). There was no difference in KIM-1, NGAL, or 2-M between four groups. In the AR group, urine FLC demonstrated the highest predictive value with sensitivity of 95.12% and specificity of 87.5% (p<0.0001). Urine FLC also performed best with a sensitivity of 96.55% and specificity of 93.33% (p<0.0001) in the ATN group. The area under the receiver operating characteristic (ROC) curves (AUC) by ROC analysis is greatest in urine RBP (100%) and FLC (99%), and lowest in KIM-1 (53.5%), then NGAL (71.5%) in the AR group. The AUC is also greatest in urine FLC (100%) and RBP (99%), and lowest in urine KIM-1 (55.6%) and NGAL (69.9%) in the ATN group. ConclusionsUrine FLC appears sensitive for both AR and ATN, and it may be a novel AKAI biomarker.