Factitious hyponatremia is most commonly associated with which of the following?

Factitious hyponatremia is most commonly associated with which of the following?

• A. Hyperlipidemia causing normal osmolality
• B. Hyperproteinemia causing normal osmolality
• C. Hyperglycemia causing high osmolality
• D. All of the above

Answer: (D)

The key idea is pseudohyponatremia, a lab artifact where the measured serum sodium is falsely low because non-aqueous substances in the blood raise the lipid or protein content and reduce the plasma water fraction. Indirect ion-selective electrodes assume a normal amount of water in plasma, so when the water fraction is reduced by high lipids or high proteins, the reported sodium concentration drops even though the sodium concentration in the water phase remains normal. Crucially, the serum osmolality stays normal in this situation, reflecting that the actual osmotic environment hasn’t changed—only the measurement artifact does. That makes hyperlipidemia and hyperproteinemia the classic associations with this phenomenon. Hyperglycemia, by contrast, increases serum osmolality and causes true hyponatremia through osmotic shifts of water between compartments, not a lab artifact from altered plasma water fraction. So it does not fit the pattern of factitious hyponatremia. Therefore, the findings most consistent with pseudohyponatremia are elevated lipids or elevated proteins with normal osmolality; the situation described by hyperglycemia represents a different mechanism and does not belong with pseudohyponatremia.

The key idea is pseudohyponatremia, a lab artifact where the measured serum sodium is falsely low because non-aqueous substances in the blood raise the lipid or protein content and reduce the plasma water fraction. Indirect ion-selective electrodes assume a normal amount of water in plasma, so when the water fraction is reduced by high lipids or high proteins, the reported sodium concentration drops even though the sodium concentration in the water phase remains normal. Crucially, the serum osmolality stays normal in this situation, reflecting that the actual osmotic environment hasn’t changed—only the measurement artifact does. That makes hyperlipidemia and hyperproteinemia the classic associations with this phenomenon.

Hyperglycemia, by contrast, increases serum osmolality and causes true hyponatremia through osmotic shifts of water between compartments, not a lab artifact from altered plasma water fraction. So it does not fit the pattern of factitious hyponatremia.

Therefore, the findings most consistent with pseudohyponatremia are elevated lipids or elevated proteins with normal osmolality; the situation described by hyperglycemia represents a different mechanism and does not belong with pseudohyponatremia.