Osmolarity is a measure of the osmoles of solute per liter of solution, while the osmolality is a measure of the osmoles of solute per kilogram of solvent . from http://en.wikipedia.org/wiki/Osmolarity Plasma osmolality Plasma osmolality is a measure of the concentration of substances such as sodium , chloride , potassium , urea , glucose , and other ions in human blood . It is calculated as the osmoles of solute per kilogram of solvent. Normal osmolality in plasma is about 280 - 303 milli-osmoles per kilogram. It is affected by changes in water content. To calculate plasma osmolarity (osmolality) use the following equation: P osm = 2[Na + ] + [Glucose]/18 + [ BUN ]/2.8 The above equation holds true if the glucose & ureas blood chemistry units are given as: mg/dL. If the units are given as: mmol/l; then the calculated osmolality is given by: P .OSM = 2[NA] + 2[K+] + [Urea] + [Glucose] Osmolality can be measured on an analytical instrument called an Osmometer....
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