In the oliguric phase of acute renal failure, which laboratory finding would most indicate reduced kidney function?

• A. Increased serum creatinine
• B. Decreased serum potassium
• C. Increased bicarbonate
• D. Decreased blood urea nitrogen

Answer: (A)

The key idea is that kidney function is best gauged by how well the kidneys can filter waste from the blood. In the oliguric phase of acute renal failure, the glomerular filtration rate (GFR) drops, so the body can’t clear waste as efficiently. Serum creatinine rises because it is produced at a constant rate and is cleared almost entirely by glomerular filtration; when GFR falls, creatinine is not cleared as well and accumulates in the blood. This makes increased serum creatinine the most direct and reliable indicator of reduced kidney function.

BUN can also rise in kidney failure, but it’s influenced by factors like hydration and protein intake, so it’s less specific. Potassium tends to increase due to impaired excretion, not decrease. Bicarbonate typically falls due to metabolic acidosis in kidney failure, so an increased bicarbonate would not fit the pattern of reduced renal function.