What is the first manifestation of nephropathy in patients with diabetes?

The first manifestation of nephropathy in patients with diabetes is microalbuminuria. This condition signifies an early stage of kidney damage where small amounts of albumin begin to leak into the urine. Microalbuminuria is typically defined as the excretion of 30 to 300 mg of albumin in a 24-hour urine sample or a urinary albumin-to-creatinine ratio of 30-300 mg/g.

Detecting microalbuminuria is crucial because it is a sign that the kidneys are starting to be affected by diabetes, and it can serve as an early indicator for the development of more serious kidney disease. Regular screening for microalbuminuria allows for timely intervention, which can help in preventing or delaying the progression of diabetic nephropathy.

The other options represent either later stages of nephropathy or conditions that do not directly relate to the initial onset of diabetic nephropathy. Kimmelstiel-Wilson nodules are associated with more advanced diabetic nephropathy, while changes in serum urea nitrogen and serum creatinine levels occur later in the disease process when significant kidney dysfunction is already established.