## **Core Concept**
The question tests knowledge on the complications associated with splenectomy, a surgical procedure to remove the spleen. The spleen plays a crucial role in filtering the blood, storing red blood cells, and supporting the immune system. Removal of the spleen can lead to various complications, and identifying the most common one requires understanding the physiological consequences of splenectomy.

## **Why the Correct Answer is Right**
The correct answer, **Infection**, particularly **overwhelming postsplenectomy infection (OPSI)**, is a well-recognized complication of splenectomy. The spleen is crucial for filtering pathogens from the blood and for the immune response. Without it, patients are more susceptible to infections, especially those caused by encapsulated bacteria like *Streptococcus pneumoniae*, *Haemophilus influenzae* type b, and *Neisseria meningitidis*. OPSI can be fatal and is a significant concern in asplenic patients.

## **Why Each Wrong Option is Incorrect**
- **Option A:** While thrombocytosis (an increase in platelet count) can occur after splenectomy due to the spleen's role in sequestering platelets, it is not typically considered a complication but rather a physiological response.
- **Option B:** Although hemorrhage is a potential immediate complication of any surgical procedure, including splenectomy, it is not the most common long-term complication.
- **Option C:** This option seems to be missing, but if it were related to another potential complication, it would still not be the most common complication compared to infections.

## **Clinical Pearl / High-Yield Fact**
A crucial point to remember is that patients who undergo splenectomy are advised to receive vaccinations against encapsulated bacteria (e.g., pneumococcal, meningococcal, and Haemophilus influenzae type b vaccines) to mitigate the risk of OPSI. Additionally, they should be educated about the signs of infection and the need for prompt medical evaluation.

## **Correct Answer:** D. Infection.