One unit of fresh blood rises the Hb% concentration by:
**Core Concept**
The increase in hemoglobin concentration after transfusion of fresh blood is determined by the hematocrit (Hct) and the volume of the transfused blood. A unit of blood is typically considered to be 300-350 mL of packed red blood cells (PRBCs) with a hematocrit of approximately 0.70-0.80.
**Why the Correct Answer is Right**
The expected increase in hemoglobin concentration after transfusion of one unit of fresh blood is a result of the addition of packed red blood cells to the recipient's circulating blood volume. The hematocrit of the transfused blood is usually higher than the recipient's native hematocrit, thereby increasing the total blood volume and subsequent hemoglobin concentration.
**Why Each Wrong Option is Incorrect**
* **Option A:** 1-2 g/dL increase is incorrect because a unit of blood typically increases hemoglobin concentration by approximately 1-2 g/dL for a 70 kg person.
* **Option B:** 3-4 g/dL increase is incorrect because this value is higher than the expected increase for a single unit of blood.
* **Option C:** 0.5 g/dL increase is incorrect because this value is lower than the expected increase for a single unit of blood.
**Clinical Pearl / High-Yield Fact**
A common mnemonic to remember the expected increase in hemoglobin concentration after transfusion of one unit of blood is: "1 unit = 1 g/dL increase for every 70 kg of body weight."
**Correct Answer: C. 1 g/dL increase for every 70 kg of body weight.**