All of the following could result in pseudohyponatremia except which?

All of the following could result in pseudohyponatremia except which?

• A. Hyperproteinemia
• B. Hypertriglyceridemia
• C. Hyperglycemia
• D. Hypercholesterolemia

Answer: (C)

Pseudohyponatremia is a lab artifact that happens when the plasma has an expanded nonaqueous phase, so the measured sodium appears lower even though the true plasma osmolality is normal. This artifact is most commonly seen when there is an excess of solids in the blood, because indirect measurement methods assume a normal plasma water fraction. Elevated proteins (hyperproteinemia) or elevated lipids (hypertriglyceridemia or hypercholesterolemia) increase the nonaqueous fraction of plasma. With indirect ion-selective electrode measurements, the sodium concentration is reported per volume of plasma, not per water fraction, so the result falsely underestimates Na+. Hyperglycemia, on the other hand, raises plasma osmolality and causes water to move from the intracellular to the extracellular space, diluting sodium. This is a true hyponatremia due to osmotic shifts, not a measurement artifact. The corrected Na+ reflects the real decrease caused by the glucose-induced water shift. So, the exception is hyperglycemia, which does not produce pseudohyponatremia.

Pseudohyponatremia is a lab artifact that happens when the plasma has an expanded nonaqueous phase, so the measured sodium appears lower even though the true plasma osmolality is normal. This artifact is most commonly seen when there is an excess of solids in the blood, because indirect measurement methods assume a normal plasma water fraction.

Elevated proteins (hyperproteinemia) or elevated lipids (hypertriglyceridemia or hypercholesterolemia) increase the nonaqueous fraction of plasma. With indirect ion-selective electrode measurements, the sodium concentration is reported per volume of plasma, not per water fraction, so the result falsely underestimates Na+.

Hyperglycemia, on the other hand, raises plasma osmolality and causes water to move from the intracellular to the extracellular space, diluting sodium. This is a true hyponatremia due to osmotic shifts, not a measurement artifact. The corrected Na+ reflects the real decrease caused by the glucose-induced water shift.

So, the exception is hyperglycemia, which does not produce pseudohyponatremia.