Calculated vs measured plasma osmolalities revisited.
The osmolalities of 100 plasma samples were measured and compared with the osmolalities calculated from the plasma concentrations (mmol/L) of sodium, potassium, glucose, and urea by several different formulae. The formula recommended by Dorwart and Chalmers (Clin Chem 21: 190, 1975) gave inferior results to those obtained with our "most accurate" formula: osmolality = 1.89 Na + 1.38 K + 1.03 urea + 1.08 glucose + 7.45. We recommend using this formula for calculation of osmolality on equipment linked to a computer. However, for simplicity, and to reduce the possibility of calculation errors, the following formula can be used for manual calculations: osmolality = 1.86 (Na + K) + glucose + urea + 10.
D001774:Blood Chemical Analysis / Q000379:methods*; D001786:Blood Glucose / Q000032:analysis; D003920:Diabetes Mellitus / Q000097:blood; D006801:Humans; D006955:Hypernatremia / Q000097:blood; D007010:Hyponatremia / Q000097:blood; D007676:Kidney Failure, Chronic / Q000097:blood; D009994:Osmolar Concentration; D011188:Potassium / Q000097:blood; D012964:Sodium / Q000097:blood; D014508:Urea / Q000097:blood
D001786:Blood Glucose; D014508:Urea; D012964:Sodium; D011188:Potassium