Osmometer: Testing Urine

An osmometer measures the osmolality of a sample. Osmolality and osmolarity are both measures of the number of solute particles, but osmolality is per kilogram of solvent, and osmolarity is per liter of solvent. Unlike specific gravity, osmolality and osmolarity don't consider solute particle size.

Urine osmolality is a measure of urine concentration. Typical values range between 50 and 1200 mOsm/kg in a healthy individual. Urine osmolality depends on the patient's hydration levels, which should be considered when interpreting the results. Low urine osmolality, less than 200 mOsm/kg, could indicate excessive hydration or diabetes insipidus. High urine osmolality, greater than 800 mOsm/kg, could indicate dehydration or diabetes mellitus.