Osmolality, Serum
| Osmolality, Serum | | | |
| Number | | 002071 |
| CPT | | 83930 |
| Synonyms | | Osmol ; Serum Osmolality |
| Special Instructions | | State patient's age on the request form. |
| Specimen | | Serum |
| Volume | | 2 mL |
| Minimum Volume | | 0.2 mL (Note: This volume does not allow for repeat testing.) |
| Container | | Red-top tube |
| Collection | | Pediatrics: Blood drawn from heelstick for capillary. Separate serum from cells as soon as possible after clot formation. Transfer specimen to a plastic transport tube. |
| Storage Instructions | | Refrigerate |
| Causes for Rejection | | Hemolysis; plasma specimen |
| Reference Interval | | Neonatal: may be as low as 266 mOsm/kg; 0-60 years: 275-295 mOsm/kg; 61 years and older: 280-301 mOsm/kg |
| 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. |
| Methodology | | Freezing point depression |
| Additional 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.1 Low serum osmolality may be secondary to overhydration, hyponatremia, syndrome of inappropriate antidiuretic hormone secretion (SIADH) with carcinoma of lung and other entities. |
| Footnotes | | - Weisberg HF, “Unraveling the Laboratory Model of a Syndrome: The Osmolality Model,” Clinician and Chemist. The Relationship of the Laboratory to the Physician, Young DS, Hicks J, Nipper H, et al, eds, Washington, DC: American Association of Clinical Chemistry, 1979, 200-43
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