Creatinine Clearance Calculator
Evaluate kidney function using Cockcroft-Gault formula for drug dosage adjustments
Frequently Asked Questions
1. What is the difference between creatinine clearance and GFR?
Creatinine Clearance (CrCl) and Glomerular Filtration Rate (GFR) both assess kidney function but are calculated differently. CrCl uses the Cockcroft-Gault formula based on serum creatinine, age, weight, and gender. GFR commonly uses MDRD or CKD-EPI formulas and considers additional factors like race. In clinical practice, values are similar, but CrCl is more often used for drug dosage adjustments, while GFR is preferred for CKD staging and diagnosis.
2. Who is the Cockcroft-Gault formula suitable for?
Suitable for adults aged 18-110, stable weight patients, and those with relatively stable kidney function. NOT suitable for pregnant women (significant muscle mass changes), severely malnourished or obese patients, amputees (reduced muscle mass), patients with acute kidney function changes, or children (use pediatric formulas). The formula requires clinical judgment for special populations.
3. How should CrCl be calculated for obese patients?
For obese patients (BMI > 30), using actual body weight may overestimate CrCl. Clinicians commonly use adjusted methods: (1) Ideal Body Weight (IBW) based on height, (2) Adjusted body weight: IBW + 0.4 × (actual weight - IBW), (3) Lean body weight for more precise estimation. Obese patient CrCl calculation should be determined by doctors or pharmacists based on individual circumstances.
4. Does normal serum creatinine mean normal kidney function?
Not necessarily. Serum creatinine levels are influenced by multiple factors: muscle mass (elderly, women, muscle atrophy patients may have lower creatinine), diet (vegetarians may have lower creatinine, high meat intake may increase it), and renal compensation (in early kidney disease, remaining nephrons can compensate by increasing filtration). Therefore, even with "normal" serum creatinine, elderly, low muscle mass, or high-risk populations should calculate CrCl or eGFR for accurate kidney function assessment.
5. Which common medications require dosage adjustment based on CrCl?
Many medications require renal dose adjustment: Antibiotics (vancomycin, aminoglycosides, some cephalosporins), Anticoagulants (dabigatran, rivaroxaban, apixaban), Diabetes medications (metformin - contraindicated if eGFR < 30), Chemotherapy drugs (carboplatin, methotrexate), Antivirals (acyclovir, ganciclovir), Analgesics (certain opioids). Specific dose adjustments should be consulted with doctors or pharmacists.
6. What are the clinical applications of creatinine clearance?
CrCl has multiple clinical applications: (1) Drug dosage adjustment - many drugs require dose adjustment based on renal function, CrCl < 30 mL/min usually needs significant adjustment. (2) Kidney function assessment - diagnosing and monitoring acute and chronic kidney disease, evaluating disease progression. (3) Contrast agent use - patients with CrCl < 60 mL/min need risk assessment and hydration to prevent contrast nephropathy. (4) Surgical risk assessment - preoperative kidney function evaluation to predict postoperative complications. (5) Dialysis indication - CrCl < 15 mL/min may require dialysis preparation. (6) Drug toxicity monitoring - certain drugs accumulate in renal insufficiency.