Which posture change is associated with hemodilution?

• A. Hemoconcentration
• B. Hemodilution
• C. No change
• D. Dehydration

Answer: (B)

Hemodilution happens when plasma volume increases relative to red cell mass, diluting blood components. Moving into a lying down (supine) posture increases venous return and allows fluid to shift from the interstitial space into the intravascular space, expanding plasma volume and lowering the concentration of red cells. This is why a person who goes from standing to lying down often shows a drop in hematocrit and appears more “diluted.” Standing or upright posture, by contrast, tends to pull fluid into the interstitial space and can cause hemoconcentration. So the posture change associated with hemodilution is lying down.