What is the typical range for viscosity of the blood?

What is the typical range for viscosity of the blood?

• A. 3 to 5
• B. 1 to 2
• C. 6 to 8
• D. 9 to 11

Answer: (A)

Viscosity is a measure of how strongly a fluid resists flowing. Blood is a non-Newtonian fluid, so its viscosity depends on shear rate and how many red cells (hematocrit) are in the blood. Under normal physiological conditions, whole blood has a viscosity of a few centipoise. The range typically cited in physiology and exams is about 3 to 5 cP. This sits above plasma viscosity (closer to 1 cP) because the cellular components increase internal friction. Because blood is shear-thinning, its viscosity decreases with increasing shear rate, so at higher flow rates it tends toward the lower end of that 3–5 cP band, while at very low flow rates it can appear higher due to red cell aggregation. The other options—1 to 2 cP or 6 to 8 cP or 9 to 11 cP—do not reflect the normal whole-blood viscosity range seen in healthy conditions; 1–2 cP is more like plasma, and 6–8 or 9–11 cP are higher than typical whole-blood values except in special low-shear scenarios. Therefore, the best answer is 3 to 5 centipoise.

Viscosity is a measure of how strongly a fluid resists flowing. Blood is a non-Newtonian fluid, so its viscosity depends on shear rate and how many red cells (hematocrit) are in the blood. Under normal physiological conditions, whole blood has a viscosity of a few centipoise. The range typically cited in physiology and exams is about 3 to 5 cP. This sits above plasma viscosity (closer to 1 cP) because the cellular components increase internal friction. Because blood is shear-thinning, its viscosity decreases with increasing shear rate, so at higher flow rates it tends toward the lower end of that 3–5 cP band, while at very low flow rates it can appear higher due to red cell aggregation. The other options—1 to 2 cP or 6 to 8 cP or 9 to 11 cP—do not reflect the normal whole-blood viscosity range seen in healthy conditions; 1–2 cP is more like plasma, and 6–8 or 9–11 cP are higher than typical whole-blood values except in special low-shear scenarios. Therefore, the best answer is 3 to 5 centipoise.