An increase in hematocrit would be expected to have which effect on peripheral resistance?

• A. Increase
• B. Decrease
• C. No change
• D. Variable

Answer: (A)

Increasing hematocrit raises blood viscosity, which raises peripheral resistance. Hematocrit is the fraction of blood that consists of red blood cells; when it goes up, blood becomes thicker and flows less easily. The resistance to flow in vessels is directly linked to viscosity, so a thicker blood requires more pressure to push it through the same vessels, meaning higher peripheral resistance. The other options don’t fit because a thicker blood does not reduce resistance, keep it the same, or vary unpredictably under normal conditions—the relationship is that increased hematocrit generally increases resistance.