Which osmolality value is consistent with an empirically calculated osmolality of approximately 270 mOsm/kg?

Which osmolality value is consistent with an empirically calculated osmolality of approximately 270 mOsm/kg?

• A. 188
• B. 204
• C. 270
• D. 390

Answer: (C)

Osmolality reflects the concentration of solute particles in serum, and the empiric calculation uses the main contributors (like sodium with the accompanying glucose and BUN) to estimate this value. When the calculated osmolality is about 270 mOsm/kg, the measured osmolality should be close to that same level in the absence of a significant osmol gap from unusual solutes. That’s why 270 mOsm/kg fits best—it sits in the normal range and aligns with the calculated value. The other numbers fall well outside the typical normal range (188 and 204 are too low, 390 is too high) and would not be consistent with an empirically calculated value of ~270.

Osmolality reflects the concentration of solute particles in serum, and the empiric calculation uses the main contributors (like sodium with the accompanying glucose and BUN) to estimate this value. When the calculated osmolality is about 270 mOsm/kg, the measured osmolality should be close to that same level in the absence of a significant osmol gap from unusual solutes. That’s why 270 mOsm/kg fits best—it sits in the normal range and aligns with the calculated value. The other numbers fall well outside the typical normal range (188 and 204 are too low, 390 is too high) and would not be consistent with an empirically calculated value of ~270.