Which statement about serum osmolality and fluid overload is true?

Which statement about serum osmolality and fluid overload is true?

• A. Low osmolality indicates dehydration.
• B. High osmolality is linked to fluid overload.
• C. Low osmolality is associated with fluid volume excess.
• D. Osmolality is not related to fluid status.

Answer: (C)

Serum osmolality reflects how concentrated the blood is with solutes, mainly sodium in combination with its anions, plus some glucose and urea. It tracks water balance: when there’s more water relative to solutes, osmolality falls; when water is scarce or solute load is high, osmolality rises. Fluid volume excess dilutes the plasma, lowering serum osmolality. Dehydration or free-water loss concentrates solutes, raising osmolality. So a low serum osmolality is associated with fluid overload, while high osmolality points toward dehydration. The other statements don’t fit: low osmolality does not indicate dehydration, high osmolality is not linked to fluid overload, and osmolality does relate to fluid status.

Serum osmolality reflects how concentrated the blood is with solutes, mainly sodium in combination with its anions, plus some glucose and urea. It tracks water balance: when there’s more water relative to solutes, osmolality falls; when water is scarce or solute load is high, osmolality rises.

Fluid volume excess dilutes the plasma, lowering serum osmolality. Dehydration or free-water loss concentrates solutes, raising osmolality. So a low serum osmolality is associated with fluid overload, while high osmolality points toward dehydration.

The other statements don’t fit: low osmolality does not indicate dehydration, high osmolality is not linked to fluid overload, and osmolality does relate to fluid status.