Test guide
Osmolality Tests
Osmolality tests measure the amount of certain substances in your blood, urine, or stool (poop). The tests can show how your kidneys are working and whether you have an unhealthy fluid balance .
What it is for
Osmolality tests may be used for a variety of reasons. A blood osmolality test , also known as a serum osmolality test, is most often used to: Sometimes, your blood plasma is also tested for osmolality by measuring the amount of sodium dissolved in it. Source: MedlinePlus, National Library of Medicine. Medical test information is public domain. Source identity and definition checked automatically on 2026-10-18. No individual clinical interpretation or human reviewer is asserted.
Limitations
Reference intervals and interpretation depend on the laboratory, specimen, method and clinical context. This source definition is educational information; it does not establish a diagnosis, product approval or suitability for an individual.
Also known as
- serum osmolality, plasma osmolality, urine osmolality, stool osmolality, osmotic gap
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