eGFR (Creatinine + Cystatin C, CKD-EPI 2021)
An estimate of how well your kidneys filter blood, worked out from both your creatinine and cystatin C levels plus your age and sex.
AI-verified against cited sources. Awaiting expert reviewAlso called eGFRcr-cys, eGFRcr-cysC, eGFR cr-cysLOINC 98980-6
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What it is
eGFR stands for estimated glomerular filtration rate, a measure of how much blood your kidneys filter each minute. This version uses two blood markers, creatinine and cystatin C, along with your age and sex. Creatinine depends partly on muscle mass and diet, and cystatin C is affected by different things, so using both usually gives a more accurate estimate than either one alone. Many labs now use the 2021 CKD-EPI equation, which does not use race.
Why it matters
KDIGO 2024 recommends this combined estimate when a creatinine-only eGFR is likely to be less accurate and the result will affect decisions, such as staging chronic kidney disease or drug dosing. It also says that if cystatin C is available, the combined estimate should be used to place kidney function into stages. Like any eGFR, one value is not enough. Chronic kidney disease needs lower kidney function or other signs of kidney damage that last at least 3 months.
If it’s low
A lower eGFR means your kidneys may be filtering less blood than expected for your age. If it stays below 60 for 3 months or more, that meets one of the standard criteria for chronic kidney disease. One low result is not enough to say that. Dehydration, illness and some medicines can lower the estimate for a while, and some conditions can shift creatinine or cystatin C without a true change in kidney function.
Common causes
- Dehydration, or a recent illness with vomiting or diarrhea (often temporary)
- Getting older, since eGFR declines gradually with age even in people without kidney disease
- Chronic kidney disease, which is more common with diabetes, high blood pressure and heart disease
- Sudden kidney injury during a serious illness (acute kidney injury)
- Higher body fat, smoking, long-term inflammation or thyroid disease, which can raise cystatin C without a drop in true filtration
- Medicines that raise creatinine or cystatin C without changing true kidney function
What can help
- Have the test repeated to confirm it, since one result is rarely enough
- Ask your clinician about a urine albumin test (uACR) alongside it
- Ask your clinician to review your medicines and supplements, and don't stop any on your own
- Keeping blood pressure and blood sugar in the range your clinician recommends supports kidney health
- Not smoking, regular physical activity and a balanced diet support kidney and heart health
If it’s high
Labs don't set an upper limit for eGFR, and young healthy adults often have estimates above 100. The combined estimate is less affected by unusual muscle mass than a creatinine-only estimate, so an unusually high number is less likely to come from low muscle mass alone.
Common causes
- Younger age, since estimates are highest in young adults
- Healthy kidney filtration
Usual ranges
What labs print as the reference range, by who was tested. Ranges differ a little between labs, so the range on your own report is the one your result is judged against.
For adults: 60 and above mL/min/1.73 m². Source: Kidney International 105(4S):S117-S314, ARUP Laboratories.
- 18+ (this one applies)60 and above mL/min/1.73 m²
Sources: Kidney International 105(4S):S117-S314, ARUP Laboratories
KDIGO 2024 GFR categories
- G5: kidney failurebelow 15 mL/min/1.73 m²
- G4: severely decreased15 to under 30 mL/min/1.73 m²
- G3b: moderately to severely decreased30 to under 45 mL/min/1.73 m²
- G3a: mildly to moderately decreased45 to under 60 mL/min/1.73 m²
- G2: mildly decreased60 to under 90 mL/min/1.73 m²
- G1: normal or high90 and above mL/min/1.73 m²
If this applies to you
eGFR (cr-cys) means a little more for some people. Open the one that fits you.
Tracking for long-term health
Creatinine depends on muscle and diet, so people who do extreme sport or bodybuilding, eat a high-protein diet or take creatine supplements can get a misleading creatinine-based eGFR. KDIGO recommends adding cystatin C when the creatinine-based result is less accurate and would affect decisions.
Age 65 or older
Cystatin C is a second kidney marker that is less tied to muscle than creatinine. KDIGO recommends an eGFR that combines both when the creatinine-based number is less accurate and the result affects decisions, such as a medicine dose.
What can affect your result
- Age: average eGFR falls gradually with age
- Muscle mass and diet, which change the creatinine part of the estimate
- Body fat, smoking, thyroid disease, steroid exposure and long-term inflammation, which change the cystatin C part
- Hydration and illness: dehydration and acute illness can lower eGFR temporarily
- Medicines that change how creatinine is handled or that affect cystatin C
- The equation your lab uses: CKD-EPI 2021 and the older 2012 combined equation give different numbers for the same samples
- Age under 18: the adult equation is not used for children
- A cooked-meat or fish meal, creatine supplements, very high-protein or very low-protein diets, and very low or very high muscle mass shift the creatinine part of the estimate. Using cystatin C as well reduces, but does not remove, this effect.
- Higher body fat, smoking, thyroid disease, steroid exposure and long-term inflammation can shift the cystatin C part of the estimate.
- KDIGO lists very low muscle mass, very high levels of inflammation, high-catabolic states and steroid use as sources of error in the combined estimate.
- The estimate assumes creatinine and cystatin C are steady from day to day. During acute illness or sudden kidney injury it is unreliable.
- Different equations (CKD-EPI 2021, the older CKD-EPI 2012 combined equation) give different numbers from the same blood sample. Compare results that come from the same equation.
Any time of day. Creatinine and cystatin C need to come from the same blood sample. Can shift within days with illness, dehydration or a meat-heavy meal. Lasting changes in kidney function are judged over at least 3 months.
When to talk to a clinician
Talk with a clinician if your eGFR is below 60, or if it has dropped by more than about 20% from your usual level (KDIGO says that is larger than the expected test-to-test variation in people with kidney disease). KDIGO lists an eGFR below 30 among the reasons to see a kidney specialist. Contact a clinician soon if a low eGFR comes with much less urine than usual, swelling in your legs or feet, nausea or vomiting, or severe tiredness. If your lab flagged the result as urgent, follow its instructions.
Questions you could ask
- Which equation does this lab use, and will my results stay comparable over time?
- How often should my kidney function be checked, given my health conditions?
- Do my creatinine and cystatin C results tell the same story about my kidney function?
- Should we repeat this test to see whether it stays low for 3 months or more?
- Should I also have a urine albumin test (uACR)?
- Could inflammation, my weight, smoking or any medicines be affecting my creatinine or cystatin C?
Questions people ask
How is this different from the eGFR on my basic metabolic panel?
The usual eGFR uses creatinine only. This version also uses cystatin C, which is affected by different things than creatinine, so it is more accurate in many situations. The two numbers can differ. In studies, 25% to 30% of people had creatinine-only and cystatin C-only estimates that were 15 mL/min/1.73 m² or 20% apart, or more (KDIGO).
Why was cystatin C added to my blood work?
Clinicians add it when a creatinine-based eGFR may be unreliable, for example with unusually low or high muscle mass, or when an accurate kidney-function number will guide decisions such as staging chronic kidney disease or dosing. Some longevity and specialty panels include it routinely.
Is one result below 60 enough to mean I have kidney disease?
No. Chronic kidney disease means lower kidney function or other signs of kidney damage that last at least 3 months. A single low value can come from dehydration, an acute illness or other short-term changes, so clinicians usually repeat the test and often add a urine albumin test (uACR).
Show the science and sources
Units
- 1 mL/min/1.73 m² = 1 mL/min/1.73 m²
- 1 mL/min/1.73 m² = 0.01667 mL/s/1.73 m²
Open the eGFR (cr-cys) unit converter
For clinicians and researchers
eGFRcr-cys (CKD-EPI 2021) = 135 × min(Scr/κ, 1)^α × max(Scr/κ, 1)^−0.544 × min(Scys/0.8, 1)^−0.323 × max(Scys/0.8, 1)^−0.778 × 0.9961^age × 0.963 [if female], where Scr is IDMS-standardized serum creatinine in mg/dL, Scys is standardized cystatin C in mg/L, κ is 0.7 (female) or 0.9 (male), and α is −0.219 (female) or −0.144 (male). Inker 2021 found that the new race-free creatinine–cystatin C equations were more accurate than the new creatinine-only equations, with smaller differences between Black and non-Black participants. KDIGO 2024 recommends eGFRcr-cys when eGFRcr is less accurate and GFR affects decisions (1C), and recommends that, in adults at risk for CKD, the GFR category be based on eGFRcr-cys when cystatin C is available (1B). Because the non-GFR determinants of the two markers differ, the combination converges on true GFR and limits the effect of either one. When eGFRcr and eGFRcys agree, accuracy is high and similar for all three estimates (estimated P30 of 87% to 91%); when they disagree, eGFRcr-cys is more accurate than either. KDIGO notes that 25% to 30% of people have gaps of 15 mL/min/1.73 m² or more, or 20% or more, between eGFRcr and eGFRcys. Sources of error in eGFRcr-cys include very low muscle mass, very high inflammation, high-catabolic states and exogenous steroid use. In pooled cohort data, eGFRcr showed a J-shaped association with risk above about 105 mL/min/1.73 m², whereas eGFRcr-cys showed much more linear associations. KDIGO Table 11 asks labs to report eGFR as a whole number relative to 1.73 m², flag values below 60 as low, and measure creatinine on the same sample as cystatin C. GFR categories are G1 90 or above, G2 60–89, G3a 45–59, G3b 30–44, G4 15–29 and G5 below 15; G1 and G2 do not meet CKD criteria without other evidence of kidney damage. KDIGO states there are not enough externally validated data to judge whether combining creatinine and cystatin C improves pediatric equations. The older 2012 combined equation differs in its constants and included a race term, so results from the two are not interchangeable.
LOINC 98980-6 (primary), 94677-2. Specimen: calculated.
Sources
- KDIGO 2024 Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease, Kidney International 105(4S):S117-S314 (2024)
- CKD-EPI Creatinine-Cystatin Equation (2021), National Kidney Foundation
- New Creatinine- and Cystatin C-Based Equations to Estimate GFR without Race, New England Journal of Medicine (2021)
- Cystatin and Creatinine With eGFR (test 3018316), ARUP Laboratories
AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.