Question 1

Should I use actual body weight or ideal body weight in the CG formula?

Accepted Answer

Use actual body weight for most patients. In severely obese patients (BMI >40), some experts recommend using adjusted body weight or lean body weight, as actual body weight can overestimate CrCl. Check local drug dosing guidelines.

Question 2

Why does the CG formula give a different number than CKD-EPI eGFR?

Accepted Answer

CG estimates CrCl in mL/min (not indexed to BSA), while CKD-EPI estimates GFR indexed to 1.73 m². Additionally, creatinine clearance includes tubular secretion of creatinine (which overestimates GFR), while CKD-EPI uses a correction for this.

Question 3

Can I use CG in patients with cirrhosis and ascites?

Accepted Answer

CG can be used but the weight-based calculation is distorted by ascites. Using dry weight or ideal body weight may be more appropriate. Cystatin C-based estimates may be preferred in cirrhosis.

Question 4

Is CG still relevant for drug dosing in the CKD-EPI era?

Accepted Answer

Yes. Many drug labels and dose adjustment tables were developed using CG. If a drug label says 'adjust dose if CrCl <30 mL/min' without specifying the equation convention, CG is the intended formula. Where both are mentioned, use CKD-EPI.