Creatinine Clearance (CrCl) Calculator

The Cockcroft-Gault equation is: CrCl (mL/min) = ((140 - age) x weight in kg) / (72 x serum creatinine in mg/dL). For female patients, multiply the result by 0.85. For example, a 60-year-old male weighing 80 kg with serum creatinine 1.2 mg/dL: CrCl = ((140-60) x 80) / (72 x 1.2) = 6400 / 86.4 = 74 mL/min.

Normal CrCl for healthy young adults is 95-135 mL/min (men) and 85-125 mL/min (women). CrCl declines by approximately 1 mL/min per year after age 40. A typical 70-year-old may have a CrCl of 60-80 mL/min even with normal serum creatinine. Values below 60 mL/min indicate significant renal impairment requiring drug dose adjustments.

CrCl (Cockcroft-Gault) and eGFR (CKD-EPI or MDRD) both estimate kidney function but serve different purposes. Most drug manufacturers reference CrCl for dosing guidelines, while CKD staging uses eGFR. CrCl slightly overestimates true GFR due to tubular creatinine secretion. They are not interchangeable, so always check whether a drug label specifies CrCl or eGFR.

In patients with BMI over 30, actual body weight can overestimate CrCl. Clinicians often use Adjusted Body Weight: AdjBW = IBW + 0.4 x (actual weight - IBW). For a 120 kg patient with IBW of 70 kg: AdjBW = 70 + 0.4 x 50 = 90 kg. Some institutions use actual weight for all patients. Check your facility protocol.

The 0.85 multiplier accounts for lower average muscle mass in women compared to men of the same age and weight. Since creatinine is a byproduct of muscle metabolism, women produce less creatinine, so the formula adjusts downward to avoid overestimating kidney function.

Common renally cleared drugs include vancomycin (target trough adjustments below CrCl 50), aminoglycosides like gentamicin and tobramycin, enoxaparin (reduce to 1 mg/kg daily when CrCl <30), dabigatran (contraindicated below CrCl 15-30), metformin (avoid below CrCl 30), and gabapentin (dose reduction below CrCl 60). Always check the specific drug label for exact thresholds.

CKD is staged by GFR/CrCl: Stage 3a (45-59 mL/min) is moderately decreased, Stage 3b (30-44) is moderately to severely decreased, Stage 4 (15-29) is severely decreased, and Stage 5 (<15 mL/min) is kidney failure requiring dialysis or transplant consideration. Many drug dose adjustments begin at Stage 3 (CrCl below 60 mL/min).

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