A 36-year-old diabetic woman develops metabolic changes following salpingo-oophorectomy. Serum osmolality of the blood can be calculated from serum values of which of the following?
**Core Concept**
The serum osmolality is a measure of the concentration of osmotically active particles in the blood, which can be calculated using the values of various serum components. In clinical practice, serum osmolality is often estimated using the formula for effective osmolality, which takes into account the contributions of sodium, glucose, and urea.
**Why the Correct Answer is Right**
The correct formula for calculating serum osmolality is: 2 x (Na+ concentration) + (glucose concentration) + (urea concentration). This formula accounts for the major osmotically active particles in the blood, including sodium ions, glucose molecules, and urea molecules. The sodium concentration is doubled to account for the fact that sodium ions contribute to the osmotic activity of the blood. The glucose and urea concentrations are added to the formula because they also contribute to the osmotic activity of the blood.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not include the contribution of sodium ions to the osmotic activity of the blood.
**Option B:** This option is incorrect because it does not include the contribution of glucose molecules to the osmotic activity of the blood.
**Option C:** This option is incorrect because it does not include the contribution of urea molecules to the osmotic activity of the blood.
**Clinical Pearl / High-Yield Fact**
When calculating serum osmolality, it's essential to remember that the formula includes the sodium concentration doubled, which accounts for the fact that sodium ions are the primary osmotically active particles in the blood.
**Correct Answer:** C. 2 x (Na+ concentration) + (glucose concentration) + (urea concentration)