What is the cause of high urine specific gravity?

The reasons for the high proportion of urine are as follows: First, insufficient blood volume or a large amount of water loss caused by prerenal oliguria, which will cause high proportion of urine, this is because the urine production is reduced, the content of various impurities in the urine is relatively high, so the proportion of urine will be correspondingly high. Third, acute glomerulonephritis or nephrotic syndrome will show a high proportion of urine, this is because such patients due to kidney disease, resulting in urine including protein and other substances content increased, so it will cause urine proportion is high.