**Core Concept**
The patient's presentation of left upper quadrant pain and a palpable spleen, combined with the peripheral smear findings, suggests a diagnosis of splenic involvement in a systemic disease. The spleen's role in filtering the blood and storing red blood cells makes it a common site for various hematological disorders.

**Why the Correct Answer is Right**
The peripheral smear is likely showing spherocytes, which are characteristic of hereditary spherocytosis (HS) or autoimmune hemolytic anemia (AIHA). However, the palpable spleen in this context is more suggestive of HS, which is an inherited disorder affecting the red blood cell membrane. The diagnosis of HS can be confirmed using immunohistochemistry (IHC) for ankyrin, which is a key protein involved in maintaining the integrity of the red blood cell membrane. Ankyrin deficiency or abnormalities are commonly seen in HS patients.

**Why Each Wrong Option is Incorrect**
**Option A:** CD20 is a marker for B cells and is used in the diagnosis of B cell lymphomas, not hereditary spherocytosis.
**Option B:** CD15 is a marker for Reed-Sternberg cells in Hodgkin lymphoma and is not relevant to the diagnosis of hereditary spherocytosis.
**Option C:** CD45 is a marker for leukocytes but is not specific for the diagnosis of hereditary spherocytosis.
**Option D:** This option is not provided, but typically, a blank or incorrect option would be labeled with a similar format.

**Clinical Pearl / High-Yield Fact**
Hereditary spherocytosis is a congenital disorder that can be inherited in an autosomal dominant or recessive pattern. It is essential to suspect HS in patients with a family history of the condition or those presenting with a palpable spleen and spherocytes on the peripheral smear.

**Correct Answer:** C.