Creatinine Clearance Calculator

Understanding Creatinine Clearance and eGFR

Creatinine clearance (CrCl) and estimated Glomerular Filtration Rate (eGFR) are measurements that indicate how well your kidneys filter waste products from the blood. Creatinine is a waste product produced by muscle metabolism — healthy kidneys filter it out efficiently. When kidney function declines, creatinine builds up in the blood. By measuring serum creatinine levels and applying validated formulas that account for age, sex, and sometimes weight, clinicians can estimate kidney function without invasive testing. An eGFR above 90 is generally normal, while below 15 indicates kidney failure potentially requiring dialysis.

Cockcroft-Gault Formula

The Cockcroft-Gault formula (1976) estimates creatinine clearance in mL/min: CrCl = [(140 − Age) × Weight (kg)] / [72 × Serum Creatinine (mg/dL)], multiplied by 0.85 for females. It remains widely used for drug dose adjustments because most pharmaceutical dosing studies were validated using this formula. However, it tends to overestimate kidney function in obese patients (because it uses actual weight) and in elderly patients. For obese patients, ideal body weight or adjusted body weight should be used instead.

CKD-EPI vs MDRD

The CKD-EPI (Chronic Kidney Disease Epidemiology Collaboration) equation, updated in 2021, is now the recommended formula for routine eGFR reporting. It's more accurate than the older MDRD formula, especially at higher GFR values (above 60). The 2021 update removed the race coefficient following controversy about its scientific basis and potential to perpetuate health disparities. The MDRD formula (Modification of Diet in Renal Disease) was the previous standard but underperforms at normal or near-normal kidney function and is being phased out in favor of CKD-EPI.

CKD Stages and What They Mean

Chronic Kidney Disease is classified into five stages based on eGFR: Stage 1 (≥90, normal but with evidence of kidney damage), Stage 2 (60–89, mildly decreased), Stage 3a (45–59, mildly to moderately decreased), Stage 3b (30–44, moderately to severely decreased), Stage 4 (15–29, severely decreased — preparation for renal replacement therapy), and Stage 5 (<15, kidney failure — dialysis or transplant typically needed). Many people with Stage 1–2 CKD are asymptomatic and diagnosed only through blood tests.

Drug Dosing in Kidney Disease

Many drugs are eliminated by the kidneys, so reduced kidney function means drugs accumulate to potentially toxic levels. Common medications requiring dose adjustment in CKD include metformin (contraindicated below eGFR 30), NSAIDs (should be avoided in CKD), certain antibiotics (gentamicin, vancomycin require therapeutic drug monitoring), digoxin, and lithium. Pharmacists and prescribing software use CrCl or eGFR to recommend appropriate dose adjustments, making accurate kidney function estimation critical for safe prescribing.