**Question:** In a post-operative patient, 21 years old with 70 kg weight, 1 unit of packed RBC will raise the hematocrit by:

A. 0.03
B. 0.05
C. 0.07
D. 0.08

**Core Concept:**

Hematocrit is a measure of the proportion of red blood cells (RBCs) in the blood. It is calculated as the volume of red blood cells divided by the total blood volume multiplied by 100%. Hematocrit is commonly used as an indicator of blood volume and volume status, particularly in cases of anemia or blood loss. RBCs are donated in units, called packed red blood cells (pRBCs), which are prepared from whole blood after removal of plasma and platelets.

**Why the Correct Answer is Right:**

The correct answer is D, 0.08. This calculation is based on the hematocrit increase following administration of a unit of packed red blood cells (pRBCs) in a 21-year-old patient weighing 70 kg. The relationship between the weight (W) of the patient, hematocrit (H) increase, and the packed red cell volume (PRCV) can be represented by the formula:

PRCV = (H x W) / 1000

Given the hematocrit increase (H) is 0.08, we can calculate the packed red cell volume (PRCV):

PRCV = (0.08 x 70) / 1000 = 0.64 / 1000 = 0.00064 L

**Why Each Wrong Option is Incorrect:**

A) 0.03: This calculation is too low, as the hematocrit increase would be too small, and the patient's hematocrit would not increase significantly.
B) 0.05: This calculation is slightly higher than the correct answer, but still not accurate enough for the given patient's weight.
C) 0.07: This calculation is too high, as the hematocrit increase would be excessive for this patient's weight and may lead to complications like pulmonary hypertension and congestive heart failure.

**Clinical Pearls:**

1. The hematocrit increase following a unit of packed red blood cells is dependent on the patient's weight, as a heavier patient will require more packed red cell units to achieve the same hematocrit increase as a lighter patient. This can help medical professionals determine the appropriate volume of packed red blood cells needed for a given patient.
2. A hematocrit increase of 0.08 is considered reasonable in a patient weighing 70 kg, as it results in a safe increase in hematocrit without causing adverse effects.
3. Adequate determination of the packed red blood cells volume required for a patient can help prevent complications and ensure a successful transfusion therapy.