The diagnosis of decreased urine specific gravity relies on urine specific gravity measurement. Urine specific gravity is mainly used to understand the concentration and dilution function of the kidneys, but also used to assist in the diagnosis of certain diseases and monitoring of the condition. Normal human urine specific gravity can be due to diet and drinking water, sweating and urination and other different situations and have large fluctuations, so the diagnosis needs to be differentiated, the following is the differential diagnosis of urine specific gravity is introduced. 1, decreased urine osmolality: urine osmolality, also known as urine osmolality, is a reflection of the number of particles of solute molecules and ions per unit volume of urine. Decrease in urine osmolality reflects the reduced concentration function of the distal tubules, which can be seen in chronic pyelonephritis, chronic interstitial lesions caused by various reasons and chronic renal failure. Increased urinary bile: urinary bile is converted from bound bilirubin. Bilirubin in the lower part of the small intestine and colon, through the role of intestinal bacteria and deconjugation, bilirubin after several stages of reduction to become urobilinogen, and then discharged with the feces. A portion of urobilinogen is absorbed from the intestine into the portal vein, most of which is taken up by the liver cells and excreted into the intestinal fluid (enterohepatic cycle), and a portion of it enters the body from the portal vein into the circulation, where it is excreted from the urine via the kidneys. A variety of factors can cause an increase in urobilinogen.