Preferred Sample Type

Urine Osmolality

Suitable Specimen Types

Plain Spot Urine

Urine Osmolality

Specimen Volume

0.5 mL

Sample Preparation

Please use a plain universal (no preservative) for this test.

Turnaround Time

1 Day (Please contact the laboratory if urgent)

Sample Processing In Laboratory

All serum and urine samples must be analysed within 24 hours of receipt into the laboratory.

Sample Stability

5 days at room temperature, 4 days at 4°C

General Information

Determination of plasma and urine osmolality are used in the assessment of electrolyte and acid-base disorders. Comparison of plasma and urine osmolalities determines the appropriateness and status of water regulation by the kidneys in settings of severe electrolyte disturbances, as might occur in diabetes insipidus or the syndrome of inappropriate secretion of antidiuretic hormone (SIADH).

For the differential diagnosis of hypo and hypernatraemia, urine electrolytes should be requested along with urine osmolality.

Patient Preparation


Reference Range

None Given


  • EQA Status: UK NEQAS Urine Chemistries Scheme
  • EQAS Scheme: Yes

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