1) an infection
2) a systemic disease or vasculitis
3) an idiopathy (usually following a flulike episode)

Other more specific precursors are polyarthritis, abscess of any internal organ, collagen vascular disease such as lupus nephritis and Henoch-Schonlein purpura, Goodpasture's syndrome, IgA nephropathy, membranoproliferative GN, anti-glomerular basement membrane antibody disease, a history of malignant tumors or blood or lymphatic system disorders, and exposure to hydrocarbon solvents.