**Core Concept**
Henoch-Schonlein Purpura (HSP) is a form of vasculitis that primarily affects small blood vessels, leading to inflammation and leakage of blood components into skin and mucosal tissues. This condition is characterized by the deposition of IgA immune complexes, which trigger an inflammatory response.

**Why the Correct Answer is Right**
The characteristic feature of HSP is the presence of non-thrombocytopenic purpura, which is a result of the vasculitis affecting the small blood vessels. One common manifestation of this vasculitis is the presence of blood in stool, also known as gastrointestinal bleeding. This occurs due to the inflammation and damage to the intestinal mucosa and blood vessels. The gastrointestinal symptoms are often accompanied by abdominal pain, nausea, and vomiting. The presence of blood in stool is a key diagnostic feature of HSP.

**Why Each Wrong Option is Incorrect**
**Option B:** Thrombocytopenia is not a characteristic of HSP. The condition is associated with normal platelet counts, and the purpura is not due to thrombocytopenia but rather due to the vasculitis.

**Option C:** Intracranial hemorrhage is a rare but serious complication of HSP, but it is not a characteristic feature of the condition. The majority of patients with HSP do not develop intracranial hemorrhage.

**Option D:** Susceptibility to infection is not a characteristic of HSP. While patients with HSP may develop complications such as kidney disease or gastrointestinal perforation, they are not more susceptible to infections.

**Clinical Pearl / High-Yield Fact**
One of the key distinguishing features of HSP from other forms of vasculitis is the presence of palpable purpura, which is a characteristic feature of the condition. This is due to the inflammation and damage to the small blood vessels, leading to the deposition of blood in the skin.

**✓ Correct Answer: A. Blood in stool**