Which value would cause the greatest concern for renal function in this CKD patient?

• A. Sodium 135 mEq/L
• B. Potassium 5.5 mEq/L
• C. Calcium 9.2 mg/dL
• D. Glomerular filtration rate 9 mL/min/1.73 m2

Answer: (D)

GFR directly measures how well the kidneys are filtering waste from the blood. A glomerular filtration rate of 9 mL/min/1.73 m2 indicates stage 5 CKD, or end-stage kidney disease, meaning there is a severe loss of filtering capacity. At this level, the kidneys cannot adequately clear toxins or manage fluids and electrolytes, leading to uremia, fluid overload, and other serious complications that often require renal replacement therapy such as dialysis or transplantation.

The other values can be normal or only mildly out of range and do not reflect the kidneys’ overall ability to filter. A sodium of 135 mEq/L is normal, a potassium of 5.5 mEq/L is mildly high and can be managed but does not by itself indicate the current level of kidney function, and a calcium of 9.2 mg/dL is within typical limits. The extremely low GFR is the most concerning indicator of renal function because it shows the kidneys have lost most of their filtering ability.