Osmolality (urine)

Code:
UOSMO

Sample Type:

Urine (random) – plain, no preservative

Minimum volume: 1 mL

Early morning sample is useful for initial investigation (>750 mOsm/kg excludes DI) .

Ref Ranges/Units:

50 – 1200 mOsm/kg 

Interpret in relation to fluid intake and hydration status. 

Turnaround:

Same Day (60 minutes from receipt for Urgent Samples)

Special Precautions/Comments:

Most useful in conjunction with serum osmolality. 

Additional Information:

Urine osmolality is a measure of dissolved, osmotically active particles (e.g. sodium, potassium, chloride, bicarbonate, urea and glucose) in the urine (i.e. how concentrated or dilute the urine is).  

Serum osmolality is carefully regulated by anti-diuretic hormone (ADH, also known as vasopressin) and thirst. These result in the concentration or dilution of urine (altering the urine osmolality). As such, urine osmolality measurements are most useful in conjunction with serum osmolality. Urine sodium is also useful if investigating the cause of hyponatraemia. 

Measurement of urine osmolality can be useful in investigation of diabetes insipidus, syndrome of inappropriate ADH (SIADH) and primary polydipsia.  

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