Osmolality, Urine

Urine osmolality is a measure of the concentration of osmotically active particles, principally sodium, chloride, potassium, urea, and glucose if present.This assay is used for assessing the concentrating ability of the kidneys. In chronic renal failure, the concentrating ability of the tubules is diminished, which may be demonstrated with a urine osmolality measurement. In polyuria due to diabetes insipidus, the urine osmolality is very low, and this may be used to differentiate this condition from polyuria of neurogenic origin.