**Core Concept**
Furosemide-induced diuresis can lead to a decrease in plasma volume, which in turn can cause a relative increase in red blood cell (RBC) concentration. This phenomenon is known as hemoconcentration.

**Why the Correct Answer is Right**
The high-dose furosemide administration in this patient resulted in a significant diuresis, leading to a substantial loss of plasma volume. As the body loses plasma, the concentration of red blood cells relative to plasma increases, causing a rise in RBC count. This is due to the dilutional effect of plasma on the RBC count being reversed, resulting in a higher concentration of RBCs in the blood.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not take into account the effect of diuresis on plasma volume. Furosemide-induced diuresis would not typically cause a decrease in RBC count.

**Option B:** This option is incorrect because it implies that the increase in RBC count is due to an increase in the actual number of RBCs, rather than a relative increase due to hemoconcentration.

**Option C:** This option is incorrect because it does not provide a plausible explanation for the increase in RBC count.

**Option D:** This option is incorrect because it implies that the increase in RBC count is due to a change in the patient's underlying condition, rather than a result of the furosemide-induced diuresis.

**Clinical Pearl / High-Yield Fact**
It's essential to consider the effect of diuresis on plasma volume when interpreting changes in blood counts. Hemoconcentration can occur in patients undergoing high-dose diuresis, leading to an apparent increase in RBC count.

**Correct Answer:** .