The onset of AP may be preceded by a headache, fever, and loss of appetite. Most patients first develop an itchy skin rash. The rash is red, either flat or raised, and may be small and freckle-like. The rash may also be larger, resembling a bruise. Rashes become purple and then rust colored over the course of a day, and fade after several weeks.
Rashes are most common on the buttocks, abdomen, and lower extremities.
Rashes higher on the body may also occur, especially in younger children. Joint pain and swelling is common, especially in the knees and ankles. About half of all patients show blood in the urine, low urine volume, or other signs of kidney involvement. Kidney failure may occur due to widespread obstruction of the capillaries in the filtering structures called glomeruli. Less common symptoms include prolonged headache, fever, and pain and swelling of the scrotum.