UTILITY OF SERUM AND URINARY FREE LIGHT CHAINS AS NON-INVASIVE BIOMARKERS OF ACTIVITY IN LUPUS NEPHRITIS

Abstract

BACKGROUND: Current laboratory biomarkers for lupus nephritis like proteinuria, urine protein to creatinine ratio, creatinine clearance, anti-ds DNA and complement levels lack sensitivity and specificity for predicting disease activity and damage. Free light chains (FLCs) released in circulation during antibodies production play a key role in the pathogenesis of autoimmune diseases. Expression of serum and urinary FLCs in lupus nephritis can act as non-invasive diagnostic and prognostic indicators and alleviate the dependency on the invasive procedure of biopsy to guide management. AIMS & OBJECTIVES: Present study intends to adjudge the implications of serum and urinary FLCs as non-invasive biomarkers of disease activity in lupus nephritis. MATERIALS & METHODS: Histomorphological diagnosis of lupus nephritis was done as per ISN-RPS classification. Cases were divided into 2 subgroups, classes I/II and III/IV in accordance with low to high histological grades and activity/chronicity scores. Concurrent serum and urinary FLCs levels were estimated by immunonephelometry and correlated with clinical presentation and histological grades of lupus nephritis. Control cases were selected from a pool of other native renal diseases with a non-immunological basis. RESULTS: Urinary kappa and lambda FLCs were significantly elevated in lupus nephritis class III/IV as compared to class I/II and controls. Serum kappa FLCs exhibited significant/near significant increments on comparison of classes III/IV and I/II with controls, however, intra-comparison of classes I/II and III/IV was insignificant. Serum lambda FLCs showed significance only for the comparison of class III/IV with controls. CONCLUSION: Urine FLCs have definite potential to be established as a non-invasive biomarker of activity in lupus nephritis. The role of serum FLCs needs further validation.