Kidney Health
Creatinine, eGFR and what kidney function tests estimate.
Kidney function is almost never measured directly. Instead it is estimated from creatinine — a waste product of muscle metabolism that healthy kidneys clear — using an equation that also accounts for age and sex. That estimate, the eGFR, is genuinely useful and genuinely approximate: it shifts with muscle mass, hydration, diet and certain medications, none of which involve the kidneys changing. This hub covers what creatinine and eGFR mean, why the race coefficient that used to appear in these equations has been withdrawn, and why a diagnosis of chronic kidney disease requires persistence over time plus a urine albumin test, never a single number.
Kidney Health tools
Calculators and converters for the measurements in this area.
eGFR
Kidney Health
Estimate kidney filtration rate with the race-free CKD-EPI 2021 equation.
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Body Surface Area
General Wellness
Calculate body surface area with four published equations, and see how far apart they land.
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Creatinine Clearance
Kidney Health
Estimate creatinine clearance with Cockcroft-Gault, and see why it differs from eGFR.
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Kidney Health guides
Plain-English explanations of what these measurements mean.
Heart HealthCardiovascular-Kidney-Metabolic Syndrome: Why Doctors Now Link the Heart, Kidneys and Metabolism
The American Heart Association now describes weight, blood sugar, blood pressure, cholesterol, kidney function and heart disease as one connected syndrome with five stages. Here…
8 min read
Kidney HealthCreatinine Clearance vs eGFR: Why Two Kidney Numbers Disagree
eGFR stages kidney function in mL/min/1.73 m², while Cockcroft-Gault creatinine clearance is in mL/min and is still used for many drug doses. They come from the same blood test…
7 min read
Heart HealthHow Heart Disease Risk Is Estimated: The PREVENT Equations Explained
The American Heart Association’s PREVENT equations estimate a person’s 10- and 30-year risk of cardiovascular disease from blood pressure, cholesterol, diabetes, smoking, age an…
8 min read
Kidney HealthBody Surface Area Formulas: Mosteller, Du Bois, Haycock and Why They Differ
Body surface area scales drug doses and kidney measurements such as eGFR. Four published equations estimate it, they agree closely at average size and diverge at higher body wei…
7 min read
Women's HealthWhich Health Calculators Do Not Apply During Pregnancy
Pregnancy changes blood volume, kidney filtration, red cell turnover and energy requirements, and most everyday health equations were derived in people who were not pregnant. He…
8 min read
Men's HealthHow Muscle Mass Distorts Creatinine, eGFR and BMI
Creatinine comes from muscle, so more muscle means a higher blood creatinine at the same kidney function — which is why eGFR equations carry a sex term. The same muscle shifts B…
8 min read
Kidney HealthWhat Is eGFR? Understanding Kidney Function
eGFR estimates how much blood your kidneys filter each minute, calculated from creatinine, age and sex rather than measured directly. A single result does not establish kidney d…
9 min read
Blood TestsHow to Read Common Blood Test Results
A reference range is built to include about 95% of a healthy population, which means roughly one result in twenty falls outside it by design. This guide explains what the most c…
9 min read
Learn this topic
Guided journeys and short quizzes. Progress is kept in your browser — no account needed.
Understand Kidney Numbers
Learn what creatinine and eGFR measure, why the equation changed, and what one result cannot establish.
4 steps
Kidney Numbers: Creatinine and eGFR
Four questions on what creatinine and eGFR measure, and what a single result can and cannot establish.
4 questions