For a serum osmolality test, which factors could affect the readings?

• A. High lipid content
• B. Fasting status
• C. Hemolysis and delayed centrifugation
• D. Exercise

Answer: (C)

Serum osmolality reflects the concentration of osmotically active particles in the plasma, so anything that changes those solutes before analysis can skew the result. When red blood cells rupture (hemolysis), intracellular components such as potassium, phosphates, and other osmoles spill into the serum, increasing the measured osmolality. If centrifugation is delayed, cells continue to metabolize in the sample, consuming glucose and producing byproducts like lactate; these changes alter the total solute balance and thus the osmolality reading. These preanalytic issues directly impact the accuracy of the measurement. Lipid content, fasting status, and exercise can affect other tests or cause variable effects, but they do not change osmolality as predictably as hemolysis and delayed processing do.