Keith D. Wrenn, MD
To the Editors: I am concerned by four problems in the article by Schelling and colleagues (1). First, the formula used to calculate osmolality is misleading. The formula used by most clinicians is as follows (2, 3):
When ethanol is included, the formula is as follows (2, 3):
If a correction for the molecular weight of urea nitrogen and glucose is not made and values measured in milliequivalents per litre or millimols per litre are plugged into the formula espoused by Schelling, osmolality is markedly overestimated. This formula may represent a typographic omission; if not, its use should be better
Wrenn KD. Osmolality. Ann Intern Med. ;114:337–338. doi: 10.7326/0003-4819-114-4-337
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Published: Ann Intern Med. 1991;114(4):337-338.
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