List two causes for the following combination of findings observed on a serum sample:
Parameter |
Patient Value |
Normal Adult Range |
Measured osmolality |
310 mOsm/L* |
280 – 290 |
Sodium |
125 mmol/L* |
135 – 145 |
Potassium |
4.0 mmol/L |
3.5 – 5.0 |
Chloride |
98 mmol/L |
95 – 105 |
Bicarbonate |
21 mmol/L* |
22 – 32 |
Glucose |
6.0 mmol/L |
4.0 – 6.0 |
Urea |
8.0 mmol/L |
3.0 – 8.5 |
Raised osmolar gap with normal AG
Mannitol
Glycine
Ethanol
Let us dissect these results systematically.
What could raise the osmolar gap but not the anion gap? Well, any osmotically active agent which is not anionic, for instance any substance which fails to dissociate at physiologic pH. Counterintuitively, virtually all toxic alcohols fall into this category, as do various soluble sugars. A high anion gap acidosis does not develop until after you have managed t metabolise a large amount of toxic alcohol into some sort of organic acid.
Thus, the list of explanations includes the following:
Kraut, Jeffrey A., and Shelly Xiaolei Xing. "Approach to the evaluation of a patient with an increased serum osmolal gap and high-anion-gap metabolic acidosis." American Journal of Kidney Diseases 58.3 (2011): 480-484.