## Core Concept
The administration of packed red blood cells (RBCs) is a common practice to increase oxygen delivery in patients with anemia or significant blood loss. The effect of packed RBC transfusion on hemoglobin levels is a critical consideration in clinical practice.

## Why the Correct Answer is Right
One unit of packed RBCs is expected to increase the hemoglobin level by approximately 1 g/dL (or 10 g/L) in a typical adult patient. This estimate assumes a patient with an average blood volume of about 70 mL/kg. The increase in hemoglobin concentration is directly related to the number of red blood cells transfused and the recipient's blood volume. The calculation can vary slightly depending on the patient's size, the hematocrit of the transfused blood, and the recipient's baseline hemoglobin and hematocrit levels.

## Why Each Wrong Option is Incorrect
**Option A:** This option suggests a much lower increase than expected. Given that one unit of packed RBCs should raise hemoglobin by about 1 g/dL, option A underestimates the effect.

**Option B:** This option suggests a higher increase than typically expected. While there can be variability, a 2 g/dL increase is generally higher than what is commonly observed with one unit of packed RBCs.

**Option D:** This option suggests a minimal effect, similar to option A but to a lesser extent. However, it still underestimates the expected increase in hemoglobin levels following the transfusion of one unit of packed RBCs.

## Clinical Pearl / High-Yield Fact
A key point to remember is that the transfusion of one unit of packed RBCs is expected to increase the hemoglobin level by approximately 1 g/dL in an average adult. This effect can vary based on patient factors, such as blood volume and baseline hemoglobin level. Clinicians often use this rule of thumb when making decisions about the need for and adequacy of RBC transfusions.

**Correct Answer:** .