Hyponatremia is defined as which of the following?

Hyponatremia is defined as which of the following?

• A. Blood sodium less than 136 mEq/L; excess of water to salt.
• B. Blood sodium over 145 mEq/L.
• C. Blood potassium over 5.1 mEq/L.
• D. Blood pH below 7.35.

Answer: (A)

Hyponatremia is a low serum sodium concentration, indicating there is more water relative to salt in the extracellular space. Normal serum sodium is roughly 135–145 mEq/L, so when it falls below about 136 mEq/L, the extracellular fluid becomes hypotonic and water shifts into cells. This dilutional effect can cause cerebral swelling and neurologic symptoms such as headache, confusion, nausea, or seizures, especially if it develops quickly or becomes severe. The other options point to different issues: high sodium means hypernatremia, not hyponatremia; high potassium is hyperkalemia; and a pH below 7.35 is acidemia, not a sodium problem.

Hyponatremia is a low serum sodium concentration, indicating there is more water relative to salt in the extracellular space. Normal serum sodium is roughly 135–145 mEq/L, so when it falls below about 136 mEq/L, the extracellular fluid becomes hypotonic and water shifts into cells. This dilutional effect can cause cerebral swelling and neurologic symptoms such as headache, confusion, nausea, or seizures, especially if it develops quickly or becomes severe. The other options point to different issues: high sodium means hypernatremia, not hyponatremia; high potassium is hyperkalemia; and a pH below 7.35 is acidemia, not a sodium problem.