Which biomarker serves as an early indicator of diabetic nephropathy?

• A. Blood urea nitrogen
• B. Creatinine clearance
• C. Microalbuminuria
• D. Urinary glucose

Answer: (C)

In diabetes, the earliest sign of kidney involvement is microalbuminuria—that is, small amounts of albumin leaking into the urine. This happens due to early glomerular injury from chronic high blood glucose and signals that the kidneys are starting to be affected. It appears before a drop in overall filtration rate or the appearance of large amounts of protein, so it’s the most sensitive early indicator. Clinically, detecting microalbuminuria (often with an albumin-to-creatinine ratio) prompts timely interventions to protect kidney function, such as tighter glycemic control and blood pressure management with ACE inhibitors or ARBs.

Blood urea nitrogen and creatinine clearance reflect kidney function and tend to change later as kidney damage progresses; BUN can be influenced by hydration and protein intake, and creatinine clearance estimates GFR but isn’t sensitive to early changes. Urinary glucose shows that blood glucose levels are high enough to exceed the kidney’s reabsorption threshold, which reflects glycemic control rather than kidney damage itself.