serum osmolality


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Related to serum osmolality: SIADH

osmolality

 [oz″mo-lal´ĭ-te]
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.

serum osmolality

The osmotic concentration of the serum.
See also: osmolality
Medical Dictionary, © 2009 Farlex and Partners
References in periodicals archive ?
Serum osmolality Urine Urine Plasma AVP (mOsm/kg) osmolality osmolality level after after DDAVP deprivation (mOsm/kg) (mOsm/kg) >300 <300 >750 <2 >300 <300 <300 >5 <290 >750 >750 2-5 >290 300-750 <750 Variable Serum osmolality Diagnosis (mOsm/kg) >300 Central DI >300 Nephrogenic DI <290 Primary polydipsia >290 Partial DI or primary polydipsia DDAVP, desmopressin; AVP, arginine vasopressin (pg/mL); DI, diabetes insipidus.
In addition to serum osmolality being a determinant of sweat rates, blood volume also affects sweat rates, albeit to a lesser extent than osmolality (Sawka et al., 1985).
The signs of SIADH in children with TBI include increased central venous pressure, low serum osmolality, low (less than 130 meq/L) serum sodium, and increased sodium in the urine with high urine osmolality.
Serum glucose 420 mg/dl, potassium 6.0 mEq/L, serum osmolality 320 mOsm/kg water.
More complex methods involving the measurement of chloride in serum and its ultrafiltrate or the measurement of serum osmolality before and after dilution have been proposed.
While the symptoms of DKA and HHS often overlap, HHS is unique in that it presents with markedly increased plasma glucose (greater than 600 mg/dl), an effective serum osmolality over 320 mOsm/kg, profound dehydration and mild to absent ketosis.1 This patient's glucose of 2040 mg/dl with a lack of urinary ketones coupled with a calculated osmolality of 365 mOsm/kg is highly suggestive of HHS.
Definitions used were: NHDKA--blood glucose >13.9 mmol/l, ketosis, serum bicarbonate < 18 mmol/l and calculated effective serum osmolality [less than or equal to] 320 mosmol/ kg; HDKA--blood glucose >13.9 mmol/l, ketosis, serum bicarbonate <18 mmol/l, and calculated effective serum osmolality >320 mosm/ kg; HHS--blood glucose >33.3 mmol/l, serum bicarbonate [greater than or equal to] 18 mmol/l, and calculated effective serum osmolality >320 mosm/ kg; and HG--blood glucose >13.9 mmol/l, serum bicarbonate [greater than or equal to] 18 mmol/l, and calculated effective serum osmolality [less than or equal to] 320 mosm/kg.
In acute hyponatremia, the brain cells are unable to compensate for the rapid decrease in serum osmolality. As such, minor increases in electrolyte-free water can lead to disproportionately large increases in intracranial pressure due to swelling of the brain cells (Arieff, Ayus, & Fraser, 1992; Hoorn, Geary, Robb, Halperin, & Bohn, 2004; Moritz & Ayus, 2003).
We are aware of one case report in the literature describing a 47-year-old woman who took an overdose of baclofen, amitryptiline and alcohol and who developed features of diabetes insipidus: polyuria, low serum osmolality and high plasma osmolality which responded to desmopressin (5).
A urine output of 300 ml/h for more than 3 h, urine specific gravity of less than 1005, serum sodium of >140 meq/l and serum osmolality of >290 mOsm/kg were taken as criteria for diagnosing diabetes insipidus (12,13).
The ranges of serum creatinine and serum osmolality in the reported cases do not differ between those who died and the survivors, Dr.

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