Turnaround Time: 1 - 3 days
CPT Code:


Test Type: 2 mL Serum or plasma
Stability Time:



Room temperature

14 days


14 days


14 days

Freeze/thaw cycles

Stable x3

Reference Range:

Neonatal: may be as low as 266 mOsm/kg; 0 to 60 years: 275-295 mOsm/kg; 61 years and older: 280-301 mOsm/kg


Evaluate electrolyte and water balance, hyperosmolar status, and hydration status; evaluate dehydration, acid-base balance; evaluate seizures; clue to alcoholism, methanol toxicity, ethylene glycol ingestion; evaluate antidiuretic hormone function, liver disease, hyperosmolar coma, evaluate hypernatremia. Osmolarity measures the concentration of particles in solution.

High serum osmolality can result from hypernatremia, dehydration, hyperglycemia, mannitol therapy, azotemia, ingestion of ethanol, methanol, ethylene glycol. Thus, osmolality has a role in toxicology and in coma evaluation. Elevated serum osmolality with normal sodium suggests possible hyperglycemia, uremia, or alcoholism.1

Low serum osmolality may be secondary to overhydration, hyponatremia, syndrome of inappropriate antidiuretic hormone secretion (SIADH) with carcinoma of lung and other entities.

1. Weisberg HF. Unraveling the laboratory model of a syndrome: The osmolality model. In: Young DS, Hicks J, Nipper H, et al, eds. Clinician and Chemist. The Relationship of the Laboratory to the Physician. Washington, DC: American Association of Clinical Chemistry;1979:200-243.

Collection Details:

Collection Instructions:

State patient's age on the request form.

Red-top tube, gel-barrier tube, or green-top (heparin) tube.

Pediatric: Blood drawn from heelstick for capillary. Separate serum or plasma from cells as soon as possible after clot formation. Transfer specimen to a plastic transport tube.