The document discusses the complexities of diagnosing diabetic nephropathy, emphasizing that renal diseases in diabetic patients can arise from multiple causes beyond diabetes. It outlines key factors and clinical indicators that should prompt further investigation, including the type of diabetes, presence of diabetic retinopathy, proteinuria patterns, and other potential complications. The necessity of renal biopsy is specified under certain conditions, especially when alternative causes of renal impairment are suspected.