Which of the following is a blood product that acts as a colloid?

• A. Plasma
• B. Lactated Ringer's solution
• C. Normal saline
• D. 5% Dextrose in water

Answer: (A)

Colloids are solutions that contain large molecules that stay mostly in the bloodstream and create an oncotic pressure that pulls fluid into the intravascular space. Plasma fits this because it has plasma proteins, especially albumin, which remain in vessels and help expand and maintain circulating volume. This makes plasma a colloid.

The other options are crystalloids, made of small molecules like electrolytes or sugars that diffuse freely across capillary walls. They rapidly distribute into the interstitial and intracellular spaces, so they don’t provide the same sustained intravascular volume expansion or oncotic effect per unit of fluid. So plasma is the blood product that acts as a colloid.