Osmolality (Serum and Urine)

Clinical Use:
Background: 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 (280-290 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.
Reference Ranges: Serum/Plasma: 280 – 290 mOsmol/Kg
Urine: 50 – 1200 mOsmol/Kg
Associated Diseases:
Patient Preparation: Urine: minimum 20ml
Specimen Requirements: Sample type:

  • Serum (SST or Red Top)
  • Urine received in plain bottle

Sample identification:

  • Three patient identifiers from
    • Name
    • D.O.B.
    • Address
    • N.H.S. number
    • Unit Number

    should match on the specimen and request form. This check may be performed prior to centrifugation by the Central Sort department.

Turnaround Time: 2 hours
Additional Information:
Referred Test: