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Plasma osmolality measures the body's electrolyte–water balance. [1] There are several methods for arriving at this quantity through measurement or calculation. Osmolality and osmolarity are measures that are technically different, but functionally the same for normal use.
The osmol gap is typically calculated with the following formula (all values in mmol/L): = = ([+] + [] + []) In non-SI laboratory units: Calculated osmolality = 2 x [Na mmol/L] + [glucose mg/dL] / 18 + [BUN mg/dL] / 2.8 + [ethanol/3.7] [3] (note: the values 18 and 2.8 convert mg/dL into mmol/L; the molecular weight of ethanol is 46, but empiric data shows that it does not act as an ideal ...
According to IUPAC, osmolality is the quotient of the negative natural logarithm of the rational activity of water and the molar mass of water, whereas osmolarity is the product of the osmolality and the mass density of water (also known as osmotic concentration). [1]
2 Calculation. 3 Interpretation. 4 ... Since osmolar clearance is given as the product of urine flow rate and the ratio of urine to plasma osmolality, this is ...
[2] 290 mOsm/kg is the presumed stool osmolality, and the measured concentration of sodium and potassium cations is doubled to account for the corresponding anions which must be present. [citation needed] A normal gap is between 50 and 100 mOsm/kg, [3] corresponding to the concentration of other solutes such as magnesium salts and sugars ...
To calculate an estimation, the total amount of substance in the body before the loss is first estimated: = where: n b = Total amount of substance before fluid loss; Osm b = Body osmolarity before loss (almost equal to plasma osmolality of 275-299 milli-osmoles per kilogram [4])
For liquid solutions, the osmotic coefficient is often used to calculate the salt activity coefficient from the solvent activity, or vice versa. For example, freezing point depression measurements, or measurements of deviations from ideality for other colligative properties, allows calculation of the salt activity coefficient through the osmotic coefficient.
Osmometry is widely used in pharmaceuticals, quality control laboratories, and clinical chemistry to measure the osmolality in aqueous solutions accurately. It is commonly used in medical clinics to assist with various pharmaceutical practices, [10] including the development of lens care solutions and eye drops.