Osmolality measures the amount of dissolved particles within the urine, which is an indirect measurement of the amount of water within the urine and the body. Dehydration results in increased concentration of particles and low fluid blood level; while too much fluid in the urine results in decreased concentration of particles. Urine osmolality is more accurate as a measurement of blood osmolality than specific gravity, and is used to diagnose kidney disease and diabetes insipidus (DI). High urine levels are seen in people with high blood sodium levels, Addison's disease, cirrhosis, CHF, or shock. Low urine levels are seen in people with high blood calcium levels, excessive fluid intake, low blood potassium levels, kidney disease, and diabetes insipidus (DI). Urine osmolality is normally run together with blood osmolality levels. The normal urine and blood osmolality ratio is 1:3.
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