An 18 year old girl presents with rash on her trunk, abdominal pain, arthritis, proteinuria and hematuria. What is the most probable diagnosis?

The key is C. HSP. [Henoch-Schönlein purpura (HSP) is an acute immunoglobulin A (IgA)–mediated disorder characterized by a generalized vasculitis involving the small vessels of the skin, the gastrointestinal (GI) tract, the kidneys, the joints, and, rarely, the lungs and the central nervous system (CNS). Rash on trunk, abdominal pain, arthritis, proteinuria and hematuria are well known features of HSP].