NAG is a lysosomal enzyme, also known as urinary enzyme. It is widely distributed in human tissues, but it is most abundant in the proximal renal tubules of the prostate and kidney. Under normal circumstances, serum N ACETYL BETA D GLUCOSAMINIDASE cannot be filtered through glomeruli and excreted from urine. Elevated urinary N ACETYL BETA D GLUCOSAMINIDASE is an early manifestation of renal disease and a sensitive indicator of renal tubular damage.