Which measurement is elevated when kidney function is reduced?

• A. Serum Urea
• B. Serum Creatinine
• C. Serum Albumin
• D. Bilirubin

Answer: (B)

Kidney function is reflected by how well waste products are cleared from the blood. When filtration drops, wastes build up. Creatinine is a waste product of muscle metabolism that is normally cleared by the kidneys. Because it is produced at a steady rate and cleared primarily by glomerular filtration, serum creatinine increases as GFR falls, making it a direct indicator of reduced kidney function. Urea (BUN) can also rise with kidney impairment, but its level is influenced by hydration and protein intake, so it’s less specific. Serum albumin is a liver-made protein and isn’t elevated by kidney dysfunction; in fact, it can decrease with certain kidney diseases due to urinary loss. Bilirubin is processed by the liver and biliary system, not the kidneys, so it isn’t a marker of reduced kidney function. Therefore, the measurement that elevates with reduced kidney function is serum creatinine.