Which statement is true regarding osmolality sample usage for measurement?

Which statement is true regarding osmolality sample usage for measurement?

• A. Only serum may be used
• B. Only plasma may be used
• C. Serum or plasma may both be used
• D. Whole blood may be used instead

Answer: (C)

Osmolality measures the concentration of solute particles in the extracellular fluid. In clinical practice, samples that accurately reflect this extracellular space are preferred, and both serum (the liquid portion after clotting) and plasma (the liquid portion with anticoagulant) provide that extracellular environment. Because they sample the same fluid compartment and, when not hemolyzed or lipemic, yield essentially the same osmolality, either can be used for measurement. Whole blood, by contrast, contains cells that contribute intracellular solutes and different water content, which skews the measurement away from true extracellular osmolality. Therefore it is not used for routine osmolality assessment. So, serum or plasma may both be used, while whole blood is not suitable.

Osmolality measures the concentration of solute particles in the extracellular fluid. In clinical practice, samples that accurately reflect this extracellular space are preferred, and both serum (the liquid portion after clotting) and plasma (the liquid portion with anticoagulant) provide that extracellular environment. Because they sample the same fluid compartment and, when not hemolyzed or lipemic, yield essentially the same osmolality, either can be used for measurement.

Whole blood, by contrast, contains cells that contribute intracellular solutes and different water content, which skews the measurement away from true extracellular osmolality. Therefore it is not used for routine osmolality assessment.

So, serum or plasma may both be used, while whole blood is not suitable.