Which of the following is an example of a colloid solution?

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

Answer: (A)

Colloid solutions use large molecules that stay inside the blood vessels and increase oncotic pressure, pulling water into the intravascular space and helping to expand circulating volume. Albumin is a natural plasma protein colloid, so it effectively enlarges the intravascular volume by retaining fluid within the vessels. The other options are crystalloids, which are composed of small molecules that readily cross capillary walls and distribute between the intravascular and interstitial compartments, providing more transient volume expansion and often requiring larger volumes. Lactated Ringer’s, normal saline, and dextrose 5% in water all behave as crystalloids (with D5W acting as free water after metabolism). Therefore, albumin is the example of a colloid solution.