**Core Concept**
Henoch-Schönlein Purpura (HSP), also known as IgA vasculitis, is a form of vasculitis that affects small blood vessels, typically presenting with a tetrad of symptoms: non-thrombocytopenic purpura, abdominal pain, arthritis, and renal involvement. The condition is characterized by the deposition of IgA immune complexes in the affected vessels.

**Why the Correct Answer is Right**
Thrombocytopenia, or low platelet count, is not a feature of Henoch-Schönlein Purpura (HSP). In fact, the condition is often associated with normal platelet counts. The purpura seen in HSP is a result of the inflammation and damage to the blood vessels, rather than a problem with platelet function or count. This distinction is crucial for making an accurate diagnosis and ruling out other conditions that may present with purpura.

**Why Each Wrong Option is Incorrect**
**Option A:** Abdominal pain is a common feature of HSP, often presenting as colicky pain in the abdomen and is a key component of the classic tetrad.

**Option B:** Splinter hemorrhage, which is characterized by small, longitudinal hemorrhages in the fingernails, can be seen in HSP and is a manifestation of the vasculitis.

**Option D:** Epistaxis, or nosebleed, can also occur in HSP, although it is less common than other symptoms like purpura and abdominal pain.

**Clinical Pearl / High-Yield Fact**
When evaluating a patient with purpura, it's essential to remember that the presence of abdominal pain and arthritis can suggest Henoch-Schönlein Purpura (HSP), and to rule out thrombocytopenia as a cause of purpura, which is more commonly associated with conditions like idiopathic thrombocytopenic purpura (ITP).

**✓ Correct Answer: C. Thrombocytopenia**