In the context of diabetic nephropathy, which type of proteinuria is more typical in early disease?

• A. Selective proteinuria.
• B. Non-selective proteinuria.
• C. No proteinuria.
• D. Tubular proteinuria only.

Answer: (A)

In the early stages of diabetic nephropathy the problem starts with the glomerular filtration barrier. Damage to the barrier reduces its ability to selectively filter proteins, and this tends to allow mainly albumin to pass into the urine. Albumin is smaller and more permeable than many larger plasma proteins, so the leakage is preferential for albumin, producing selective proteinuria. This pattern often manifests as microalbuminuria, an early sign of renal involvement in diabetes. As the disease progresses and the barrier loses more of its selectivity, protein excretion becomes non-selective, involving larger proteins as well. Tubular proteinuria would point to tubular dysfunction, which is not the typical early pattern in diabetic nephropathy. And no proteinuria would miss the initial albumin leakage that characterizes early disease.