The formula for calculating Creatinine Clearance is
((140-age)*(ideal body weight in kg)) /((serum creat)*(72)) for men; times 0.85 for a female.
If they are enormously obese use your own fudge (low fat I hope) factor. I like to add an additional 20% to compensate for the ideal body weight.
Creatinine Clearance Calculator
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