Osmolality is a physical property dependant upon the total number of solute particles present in a solution and whether or not they penetrate cell membranes. In health the serum osmolality is maintained within a close range (275-295 mosmol/kg). This is achieved by controlling water input, by thirst and water output by ADH control in the kidneys. Urine osmolality will vary more widely as the renal water loss is adjusted to maintain normal serum levels.
Serum: 275 – 295 mOsmol/Kg
Urine: 50 – 1200 mOsmol/Kg
Urine: minimum 20ml
- Serum (SST yellow top tube)
- Urine received in plain bottle