Uremia mainly refers to the patients due to various reasons for renal tubular concentration dysfunction, the emergence of renal tubular water reabsorption dysfunction leads to the patients to excrete a large amount of urine, the patients are mainly manifested as thirst, irritability, polydrinking, polyuria and other symptoms, which can be diagnosed through the examination of urinary routine and urine osmolality. Usually when measuring urine osmolality, it is necessary to measure plasma osmolality at the same time for the ratio, at this time it is easier to differential diagnosis of uremia. Mainly include the following checks: 1, urine specific gravity: uremic patients typical characteristics of urine specific gravity is low, usually less than 1.01 × 1.00, due to uremic patients urinate a large amount of urine, so that water is not reabsorbed by the renal tubules, a large amount of water through the urine filtration, which can lead to the patient’s discharge of urine with a lower urine specific gravity. For patients with uremia when checking urine routine, it can be observed that the discharged urine is low specific gravity urine, which is a typical feature; 2, urine osmolality: under normal circumstances, urine osmolality is 600-1000mOsm/kg-H2O, the 24-hour range of change is generally in the range of 400-1400mOsm/kg-H2O, the ratio of urine osmolality and plasma osmolality is about in the (3-4):1, patients with uremia Urine osmolality will be significantly lower than the normal reference range.