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Osmolality, urine

Lab area
Clinical Biochemistry - General
Method and equipment
Freezing Point Depression
Expected turn-around time
STAT/ Urgent: 1 Hour Routine: 1 Hour
Specimen type

Serum or Sodium/Lithium Heparin plasma/ Urine/ Pharmacy Fluids

Specimen requirements

60 uL

Storage and transportation


Shipping information
The Hospital for Sick Children
Rapid Response Laboratory
555 University Avenue, Room 3642
Toronto, ON
M5G 1X8
Phone: 416-813-7200
Toll Free: 1-855-381-3212
Hours: 7 days/week, 24 hours/day
Background and clinical significance

Clinical uses of serum osmolality include screening for toxin ingestion (alcohols, glycols), monitoring concentration of osmotically active agents (eg., mannitol), and evaluation of hyponatremia (exclusion of pseudohyponatremia, presence of other osmotic agents such as glycine and glucose). Clinical uses of urine osmolality include evaluation of increased urine output (as in primary polydipsia, diabetes insipidus, diabetes mellitus), evaluation of decreased urine output (dehydration, acute tubular injury), and evaluation of renal acidification defects. Stool osmolality may be used to separate secretory diarrhea (due to agents damaging the mucosa) from osmotic diarrhea (due to the presence of unabsorbed solutes, laxative abuse, malabsorption).

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