Urinary NAG, known as urinary N-acetyl-beta-D-aminoglucosidase, is an intracellular lysosomal enzyme that is generally highest in the proximal tubule of the renal tubule. If there is a high level, the most common cause is injury to the renal tubules, such as our common renal tubular acidosis or tubular necrosis, which can lead to high urinary NAG enzyme. In addition, because urinary NAG it is involved in the metabolism of sugar, it also has obvious diagnostic significance for the early stage of diabetic nephropathy. In addition, high urinary NAG enzyme can also be seen in patients with upper urinary tract infection, that is, acute pyelonephritis, which helps to distinguish the localization of urinary tract infection, whether it is upper or lower urinary tract infection.