A patient presents with hematuria of several days and dysmorphic RBC casts in urine. The site of origin is:

Isolated microscopic hematuria with dysmorphic RBC casts can be a manifestation of glomerular diseases. The RBCs of glomerular origin are often dysmorphic when examined by phase-contrast microscopy. Irregular shapes of RBCs may also result from pH and osmolarity changes produced along the distal nephron. The most common etiologies of isolated glomerular hematuria are IgA nephropathy, hereditary nephritis, and thin basement membrane disease. IgA nephropathy and hereditary nephritis can lead to episodic gross hematuria. Isolated hematuria without proteinuria, other cells, or casts is often indicative of bleeding from the urinary tract. Ref: Cooper C.S., Joudi F.N., Williams R.D. (2010). Chapter 38. Urology. In G.M. Dohey (Ed), CURRENT Diagnosis & Treatment: Surgery, 13e.