Which equation gives serum osmolality?

Unlock all questions

This demo includes only 20 questions. Upgrade to access hundreds of questions, flashcards, exam simulations, and disable ads.

Full question bankExam simulationsFlashcards
From $25.99Unlock all

Prepare for the NBME Form 11 Test with targeted flashcards and multiple-choice questions. Each question includes hints and explanations to aid learning. Boost your readiness for exam day!

Multiple Choice

Which equation gives serum osmolality?

Explanation:
Serum osmolality is determined by the concentration of osmotically active particles in the blood. The major driver is sodium, because most serum solutes are sodium salts with accompanying anions. To reflect the contribution of sodium plus its accompanying ions, you multiply sodium by 2. The other important contributors are glucose and urea nitrogen (BUN), each added after converting to the same molar units: glucose in mg/dL is divided by 18 to convert to mmol/L, and BUN in mg/dL is divided by 2.8 to convert to mmol/L. Put together, the estimated serum osmolality is 2 × Na + glucose/18 + BUN/2.8, giving units of mOsm/kg. This formulation is more accurate than using Na alone or using different conversion constants (like 3 or 2.5 for BUN) because it properly accounts for the osmotic contributions and unit conversions.

Serum osmolality is determined by the concentration of osmotically active particles in the blood. The major driver is sodium, because most serum solutes are sodium salts with accompanying anions. To reflect the contribution of sodium plus its accompanying ions, you multiply sodium by 2. The other important contributors are glucose and urea nitrogen (BUN), each added after converting to the same molar units: glucose in mg/dL is divided by 18 to convert to mmol/L, and BUN in mg/dL is divided by 2.8 to convert to mmol/L. Put together, the estimated serum osmolality is 2 × Na + glucose/18 + BUN/2.8, giving units of mOsm/kg. This formulation is more accurate than using Na alone or using different conversion constants (like 3 or 2.5 for BUN) because it properly accounts for the osmotic contributions and unit conversions.

More Multiple Choice Questions
Subscribe

Get the latest from Passetra

You can unsubscribe at any time. Read our privacy policy