What are the raw creatinine clearance and the body surface area–adjusted creatinine clearance for a 57‑year‑old male who weighs 126 lb (≈57 kg), is 65 in (≈165 cm) tall, has a serum creatinine of 2.10 mg/dL (impaired renal function), a 24‑hour urine volume of 1900 mL, and a urine creatinine concentration of 602 mg/dL?

Creatinine Clearance Calculation

For this 57-year-old male patient, the raw (unadjusted) creatinine clearance is 54.5 mL/min and the BSA-adjusted creatinine clearance is 59.8 mL/min/1.73 m², indicating moderate renal impairment (CKD Stage 3).

Calculation Method

The 24-hour urine creatinine clearance is calculated using the standard formula 1:

Raw CrCl = (Urine Creatinine × Urine Volume) / (Serum Creatinine × Time in minutes)

Step-by-Step Calculation:

Raw Creatinine Clearance:

• Urine creatinine: 602 mg/dL
• Urine volume: 1900 mL = 19 dL
• Serum creatinine: 2.10 mg/dL
• Collection time: 24 hours = 1440 minutes

Raw CrCl = (602 mg/dL × 19 dL) / (2.10 mg/dL × 1440 min) Raw CrCl = 11,438 / 3,024 Raw CrCl = 54.5 mL/min 1

BSA-Adjusted Creatinine Clearance:

First, calculate BSA using the DuBois formula:

• Weight: 126 lb = 57.2 kg
• Height: 65 inches = 165 cm

BSA = 0.007184 × (165^0.725) × (57.2^0.425) = 1.66 m²

BSA-adjusted CrCl = Raw CrCl × (1.73 m² / Patient's BSA) BSA-adjusted CrCl = 54.5 × (1.73 / 1.66) BSA-adjusted CrCl = 59.8 mL/min/1.73 m² 1

Clinical Interpretation

• This patient has significantly impaired renal function with a measured creatinine clearance below 60 mL/min/1.73 m², which should be flagged as low per KDIGO 2024 guidelines 1

• The 24-hour urine collection for measured creatinine clearance is appropriate when estimated GFR equations are thought to be inaccurate, as recommended by KDIGO when measured GFR is not available 1

• The serum creatinine of 2.10 mg/dL alone would underestimate the degree of renal dysfunction compared to the measured clearance, as serum creatinine can remain in the "normal" range despite significantly decreased GFR 2

Important Clinical Caveats

• The 24-hour collection must be complete and accurate for these calculations to be valid 3, 4. Incomplete collections will underestimate true clearance.

• This measured clearance should guide medication dosing adjustments for renally eliminated drugs, as it provides a more accurate assessment than serum creatinine alone in this patient with moderate renal impairment 2, 5

• Estimated GFR equations consistently overestimate renal function compared to measured clearance, particularly near clinically significant thresholds like 60 mL/min/1.73 m² 6, making this measured value particularly important for therapeutic decisions

• The BSA-adjusted value (59.8 mL/min/1.73 m²) should be used for clinical staging and comparison to reference ranges, while the raw value (54.5 mL/min) may be more appropriate for certain drug dosing calculations 1, 7