II. Definitions
- Osmolality
- Total solute concentration in a fluid compartment
- Tonicity
- Concentration of osmoles in a compartment that generate osmotic pressure gradient
- Tonicity impacts water traversal from one compartment to another
- Only solutes that cannot move freely between compartments generate an osmotic gradient
- Blood Urea Nitrogen (BUN) does not affect tonicity, but does influence osmolality
- BUN crosses easily between compartments and does not generate an osmotic gradient
- Extracellular Fluid Tonicity is based on only a few effective osmoles (of which Sodium is key)
- Sodium concentration (primary)
- Glucose (severe Hyperglycemia in Diabetes Mellitus)
- Mannitol or Sorbitol (used to decrease Intracranial Pressure in closed Head Trauma)
III. Interpretation: Normal
- Serum Osmolality: 280-300 mOsm/(kg water)
IV. Calculation: Calculated Serum Osmolality
- Serum Osms = 2*Na + Glu/18 + BUN/2.8 + Et/4.6 + Man/18
- Annotation
- Where Na is Serum Sodium
- Where Glu is Serum Glucose
- Where BUN is Blood Urea Nitrogen
- Where Et is Blood Alcohol Level
- Where Man is Mannitol
V. Causes: Increased Serum Osmolality
VI. Causes: Decreased Serum Osmolality
- SIADH
- Hyponatremia
- Overhydration
VII. References
Calculation (FPnotebook.com: DrBits) Open in New Window
Images: Related links to external sites (from Bing)
Related Studies
| Concepts | Laboratory Procedure (T059) |
| SnomedCT | 166719000, 144008001, 44628004 |
| English | Serum osmolality, serum osmolality, serum osmolality (lab test), Serum osmolality measurement, serum osmolality test, Serum osmolality (& level), Serum osmolality (& level) (procedure), Serum Osmolality Test, Osmolality measurement, serum, Osmolality measurement, serum (procedure) |
| Dutch | serumosmolariteit |
| French | Osmolalité sérique |
| German | Osmolalitaet des Serums |
| Italian | Osmolalità sierica |
| Portuguese | Osmolalidade sérica |
| Spanish | Osmolalidad del suero, medición de osmolalidad en suero (procedimiento), medición de osmolalidad en suero |
| Japanese | 血清浸透圧, ｹｯｾｲｼﾝﾄｳｱﾂ |
| Czech | Osmolalita séra |
| Hungarian | Szérum ozmolaritás |
Ontology: Blood osmolarity (C0596196)
| Definition (CSP) | measures moles per liter of blood; increases with dehydration and decreases with overhydration; normal osmolarity is contributed to mostly by sodium, chloride, potassium, urea and glucose, as well as other ions and substances in the blood. |
| Concepts | Laboratory Procedure (T059) |
| Italian | Osmolarità ematica |
| Japanese | 血液浸透圧, ｹﾂｴｷｼﾝﾄｳｱﾂ |
| Czech | Osmolarita krve |
| English | Blood osmolarity, blood osmolarity, osmolarity blood |
| Hungarian | Vér ozmolaritás |
| French | Osmolarité sanguine |
| Portuguese | Osmolaridade do sangue |
| Spanish | Osmolaridad de la sangre |
| Dutch | bloedosmolariteit |
| German | Osmolaritaet des Blutes |
Ontology: tonicity disorder (C0679318)
| Concepts | Pathologic Function (T046) |
| English | tonicity disorder |
