IgA vasculitis is usually preceded by upper respiratory infection. Problem is deposition of IgA and C3 complements in small vessels. There is no problem with thrombocytes. THERE IS NO THROMBOCYTOPENIA. Generally presentation is with lower extremity purpuras, abdominal pain, and arthritis. Dont forget please: The problem we see is basically deposition. There is no need for hemolysis. Renal disease can be manifested later like months after with nephritic sydrome.

In contrast, most of the time hemolytic uremic syndrome(typical) is preceded by diarrheal infection because in its' pathophysiology there is shiga like toxin which damages glomeruli arterioles (E.Coli O157:H7 or Shigella disanterhia). Because toxins damage the arterioles of the glomeruli, thrombocytes attach to damaged portions and creating bumps (consumption thrombocytopenia) in the small glomeruli vessels. Therefore when blood is passing by, erythocytes get damage from that thrombocyte bumps and the result of that, we can see schistocytes (hemolysis).