<unk>  is a measurement of the concentration of<unk>  in the urine. The<unk>  is expressed as a concentration (such as millimoles per liter). The result must therefore be interpreted in the context of the degree of urine concentration present. Alternatively, the<unk>  can be standardized to the excretion of creatinine using a formula such as the fractional excretion of<unk>  (FENa). Because the hypothalamus/osmoreceptor system ordinarily works well to cause drinking or urination to restore the body's<unk>  concentrations to normal, this system can be used in medical treatment to regulate the body's total fluid content, by first controlling the body's<unk>  content. Thus, when a powerful diuretic drug is given which causes the kidneys to excrete<unk> , the effect is accompanied by an excretion of body water (water loss accompanies<unk>  loss). This happens because the kidney is unable to efficiently retain water while excreting large amounts of<unk> . In addition, after<unk>  excretion, the osmoreceptor system may sense lowered<unk>  concentration in the blood and then direct compensatory urinary water loss in order to correct the hyponatremic (low blood<unk>  state.
Urine sodium
Urine osmolality
Serum chloride
Blood urea nitrogen
Plasma osmolality
Urine urea nitrogen
Urine flow rate
Urine anion gap