Osmolality, Serum

Test ID:

703060

CPT code:

83930

Synonyms:

Osmolality

Clinical Use:

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.

Test Information:

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

Specimen Type:

Serum or plasma

Requested Volume:

2 mL

Minimum Volume:

0.2 mL

Container Type:

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

Collection:

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