A formula approximating the osmolality of blood serum is referred to as

A formula approximating the osmolality of blood serum is referred to as

• A. Isotonic
• B. Hypotonic
• C. Hypertonic
• D. Osmolar

Answer: (A)

Understanding how we label a calculation of serum osmolality is key. The body’s osmolality reflects the concentration of osmotically active particles, and clinicians estimate it with a formula that uses routinely measured values like sodium, glucose, and BUN (for example, calculated serum osmolality ≈ 2 × Na + glucose/18 + BUN/2.8). The term that names this calculation is osmolar (or osmolarity). Isotonic, hypotonic, and hypertonic describe how a solution’s osmolality compares to plasma, not the name of the calculation itself. So the best fit is osmolar.

Understanding how we label a calculation of serum osmolality is key. The body’s osmolality reflects the concentration of osmotically active particles, and clinicians estimate it with a formula that uses routinely measured values like sodium, glucose, and BUN (for example, calculated serum osmolality ≈ 2 × Na + glucose/18 + BUN/2.8). The term that names this calculation is osmolar (or osmolarity). Isotonic, hypotonic, and hypertonic describe how a solution’s osmolality compares to plasma, not the name of the calculation itself. So the best fit is osmolar.