Glomerulonephritis is a kidney disease defined by the presence of inflammation in the kidney's filtering system (glomeruli). The inflammation causes protein and red blood cells to flow into the urine while toxins that the kidney normally filters are kept in the body. There are different causes of glomerulonephritis. In some instances, it can be caused by infections such as strep throat or autoimmune disorders such as lupus. In other cases, no cause can be identified.