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the concentration of a solution in terms of osmoles of solutes per kilogram of solvent.
serum osmolality a measure of the number of dissolved particles per unit of water in serum. In a solution, the fewer the particles of solute in proportion to the number of units of water (solvent), the less concentrated the solution. A low serum osmolality means a higher than usual amount of water in relation to the amount of particles dissolved in it, and accompanies overhydration, or edema. An increased serum osmolality indicates deficient fluid volume. Measurement of the serum osmolality gives information about the hydration status within the cells because of the osmotic equilibrium that is constantly being maintained on either side of the cell membrane (homeostasis). Water moves freely back and forth across the membrane in response to the osmolar pressure being exerted by the molecules of solute in the intracellular and extracellular fluids. Serum osmolality reflects the status of hydration of the intracellular as well as the extracellular compartments and thus describes total body hydration. The normal value for serum osmolality is 270–300 mOsm/kg water.
urine osmolality a measure of the number of dissolved particles per unit of water in the urine. A more accurate measure of urine concentration than specific gravity, urine osmolality is useful in diagnosing renal disorders of urinary concentration and dilution and in assessing status of hydration. The normal value is 500 to 800 mOsm/L.
Miller-Keane Encyclopedia and Dictionary of Medicine, Nursing, and Allied Health, Seventh Edition. © 2003 by Saunders, an imprint of Elsevier, Inc. All rights reserved.
os·mo·lal·i·ty(oz'mō-lal'i-tē), Do not confuse this word with osmolarity.
The concentration of a solution expressed in osmoles of solute particles per kilogram of soluent.
Farlex Partner Medical Dictionary © Farlex 2012
osmolalityToxicology A measure of the amount of osmotically effective solute/1000 g of solvent; serum osmolality is↑ in Ethanol, azotemia, dehydration, DM, hypercalcemia, hyperglycemia, hypernatremia, ethylene glycol, glycerine, INH, ketosis, mannitol therapy, methanol, pyelonephritis, renal tubular necrosis, diabetes insipidus, shock, sorbitol, uremia ↓ in Overhydation, ↑ fluid intake, ↓ Na+, paraneoplastic syndrome, SIADH; urine osmolality is ↑ in SIADH, liver disease, heart disease, dehydration ↓ in Overhydration, diabetes insipidus, ↓ K+ Ref range Serum, 275-295 mOsm/Kg; urine 50–1400 mOsm/Kg Critical (panic) values ≤ 265 mOsm/Kg; ≥ 320 mOsm/Kg. See Delta osmolality, Effective osmolality.
McGraw-Hill Concise Dictionary of Modern Medicine. © 2002 by The McGraw-Hill Companies, Inc.
The concentration of a solution expressed in osmoles of solute particles per kilogram of solvent.
Medical Dictionary for the Health Professions and Nursing © Farlex 2012
osmolalityThe property of a solution that depends on its concentration in osmolal units. See OSMOLE.
Collins Dictionary of Medicine © Robert M. Youngson 2004, 2005
A measurement of urine concentration that depends on the number of particles dissolved in it. Values are expressed as milliosmols per kilogram (mOsm/kg) of water.
Gale Encyclopedia of Medicine. Copyright 2008 The Gale Group, Inc. All rights reserved.