GFR Calculator

Enter your serum creatinine from a recent blood test, in mg/dL as used in the US or µmol/L as used in many other countries, along with your age and sex. The result is reported in milliliters per minute per 1.73 m² of body surface area, the standard way to compare kidney function between people of different sizes.

What is Glomerular filtration rate (GFR)?

Each kidney contains about a million tiny filtering units called nephrons. At the start of each one is a glomerulus, a knot of capillaries that filters water, salts and waste out of the blood while holding back blood cells and most proteins. Glomerular filtration rate is the total volume of blood plasma filtered by all the glomeruli each minute. It is the best overall measure of kidney function. A healthy young adult filters roughly 120 mL a minute, and GFR declines slowly with age. A low GFR means waste products build up in the blood, and it is used to detect, stage and monitor chronic kidney disease and to adjust the doses of drugs cleared by the kidneys.

Population Mean Estimated GFR

Average eGFR falls gradually with age, as these National Kidney Foundation figures show.

Chronic Kidney Disease Stages

Chronic kidney disease means kidney damage or reduced kidney function lasting more than three months. The international KDIGO guidelines, endorsed by the National Kidney Foundation, sort it into categories by GFR. An eGFR of 60 or more counts as CKD only when there are other signs of damage, most often albumin in the urine, so doctors also check a urine albumin-to-creatinine ratio. CKD often causes no symptoms until it is advanced, which is why people with diabetes, high blood pressure, heart disease, a family history of kidney failure or age over 60 are advised to get tested. The CDC estimates that more than 1 in 7 US adults has CKD and most do not know it.

Measuring GFR

GFR cannot be measured directly in a person. A measured GFR is obtained by injecting a substance that the kidneys filter but do not reabsorb or secrete, such as inulin, iohexol or iothalamate, and tracking how fast it is cleared from blood or urine. This is accurate but slow and costly, so it is reserved for research and special cases such as evaluating kidney donors.

In everyday practice GFR is estimated from creatinine, a waste product made at a fairly steady rate by muscle and removed almost entirely by the kidneys. When kidney function falls, creatinine rises in the blood. Because creatinine also depends on muscle mass, diet and age, equations adjust for age and sex to turn a creatinine level into an estimated GFR. Labs in the US now report eGFR automatically with most metabolic panels.

The CKD-EPI equation, developed by the Chronic Kidney Disease Epidemiology Collaboration, is the standard for adults. Its 2009 version and the older MDRD (Modification of Diet in Renal Disease) equation included a multiplier for Black race. In 2021 a joint task force of the National Kidney Foundation and the American Society of Nephrology recommended a refitted CKD-EPI equation that does not use race, and US laboratories have widely adopted it. This calculator shows the 2021 result first and the older equations for comparison. MDRD tends to underestimate GFR above about 60, which is one reason CKD-EPI replaced it.

Some situations make creatinine-based estimates unreliable: very high or very low muscle mass, amputations, vegetarian diets or creatine supplements, pregnancy, severe illness and rapidly changing kidney function. In these cases doctors may add a blood test for cystatin C, another filtration marker that depends less on muscle, and use a combined creatinine-cystatin C equation, or measure creatinine clearance from a 24-hour urine collection.

Children have their own equations because their body size and muscle mass change as they grow. The bedside Schwartz equation, published in 2009, multiplies height in centimeters by 0.413 and divides by serum creatinine in mg/dL. For drug dosing, pharmacists sometimes still use the Cockcroft-Gault creatinine clearance estimate, which includes body weight.

A single result should not be over-interpreted. Creatinine can rise temporarily with dehydration, a large meat meal or intense exercise, so an abnormal eGFR is usually repeated. Talk to your doctor about what your numbers mean and whether you need further tests.

CKD-EPI 2021: eGFR = 142 × min(SCr/κ, 1)^α × max(SCr/κ, 1)^−1.200 × 0.9938^Age × 1.012 [if female]

SCr

serum creatinine in mg/dL (µmol/L ÷ 88.4)

κ

0.7 for females, 0.9 for males

α

−0.241 for females, −0.302 for males

MDRD: 175 × SCr^−1.154 × Age^−0.203 × 0.742 [female] × 1.212 [Black]. CKD-EPI 2009 uses 141, α of −0.329 (female) or −0.411 (male), exponent −1.209, 0.993^Age, × 1.018 [female] and × 1.159 [Black]. Bedside Schwartz (children): 0.413 × height (cm) ÷ SCr.

Frequently asked questions

Sources

• National Kidney Foundation
• NIH NIDDK – Kidney Disease
• CDC – Chronic Kidney Disease