CD79A and purpura: In 2019, the Single Hub and Access point for pediatric Rheumatology in Europe Initiative established the diagnostic criteria for HSP, emphasizing the presence of purpura or petechiae predominantly on the lower limb with 1 of 4 conditions: (1) abdominal pain; (2) histopathology (IgA); (3) arthritis or arthralgia; and (4) renal involvement.[8] Purpura or petechia serve as essential markers for diagnosis.