Rosh Internal Medicine Boost Practice Exam

In a case of hypertonic hyponatremia, which laboratory value is likely elevated?

1. Serum glucose

2. Serum potassium

3. Serum sodium

4. Serum triglycerides

The correct answer is: Serum glucose

In hypertonic hyponatremia, the most likely laboratory value to be elevated is serum glucose. Hypertonic hyponatremia typically occurs in situations where there is an increase in the osmotic activity of substances other than sodium, most commonly glucose in cases of uncontrolled diabetes mellitus or high glucose infusions. When serum glucose levels rise significantly, it can draw water out of the cells into the extracellular space, diluting the sodium concentration despite the total body sodium possibly being normal or even elevated. This dilution effect leads to a lower measured sodium concentration in the serum, hence the term "hyponatremia." Higher serum glucose effectively means that there are more osmoles in the blood, which influences the distribution of water and can manifest as a reduction in serum sodium levels. Therefore, in the context of hypertonic hyponatremia, it is the elevated serum glucose that is instrumental in this condition. Other options like serum potassium, sodium, and triglycerides do not share this direct association with hypertonic states induced by conditions like high blood sugar, making serum glucose the most relevant and elevated laboratory value in cases of hypertonic hyponatremia.