Sanjeev Sethi, M.D., Ph.D., explains Mayo Clinic Laboratories’ newly developed test to detect neural epidermal growth factor-like 1 protein (NELL-1), a biomarker for membranous nephropathy (MN). The immunohistochemistry assay examines tissue samples for NELL-1 antigen, which are found in 10% to 15% of MN patients. Discovered by Dr. Sethi in 2017, NELL-1 is the second most common antigen associated with MN and is correlated with underlying malignancy.