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eGFR (Cystatin C-based)

An estimate of how well your kidneys filter blood, worked out from your cystatin C level, age and sex, without using creatinine.

AI-verified against cited sources. Awaiting expert reviewAlso called eGFRcys, eGFR cys, eGFRcysCLOINC 50210-4

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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 is calculated from your blood cystatin C level, your age and your sex. Cystatin C does not depend much on muscle mass, so it can be a useful alternative when creatinine may be misleading. It does have its own influences, such as body fat, smoking, inflammation and thyroid problems.

Why it matters

A cystatin C-based eGFR can help when a creatinine-based eGFR is likely to be off, for example in healthy people with an unusual amount of muscle. KDIGO 2024 suggests considering it in specific circumstances. It adds that using creatinine and cystatin C together (a combined eGFR) is more accurate than either alone, and it recommends the combined estimate when creatinine alone is less accurate. A large gap between the two single-marker estimates can be informative on its own.

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. Cystatin C can also be raised by body fat, smoking, inflammation and an overactive thyroid, which can make the estimate look lower than your true 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 an overactive thyroid, which can raise cystatin C without a drop in true filtration
  • Steroid medicines or excess natural cortisol

What can help

  • Have the test repeated to confirm it, since one result is rarely enough
  • Ask your clinician whether a creatinine-based eGFR and a combined creatinine-plus-cystatin C eGFR agree with it
  • Ask your clinician about a urine albumin test (uACR) alongside it
  • 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. Cystatin C is influenced by things other than the kidneys, and a lower cystatin C gives a higher eGFR, so a high number does not always mean stronger kidneys.

Common causes

  • Younger age, since estimates are highest in young adults
  • Healthy kidney filtration
  • An underactive thyroid, which can lower cystatin C without a change in true 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: Mayo Clinic Laboratories (via the Schneck Medical Center test catalog), Kidney International 105(4S):S117-S314.

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

What can affect your result

  • Age: average eGFR falls gradually with age
  • Body fat, smoking, thyroid disease, steroid exposure and long-term inflammation
  • Hydration and illness: dehydration and acute illness can lower eGFR temporarily
  • The cystatin C assay and the equation your lab uses
  • Age under 18: adult equations are not used, and pediatric equations apply
  • Higher body fat, smoking, thyroid disease, steroid exposure and long-term inflammation (such as a raised CRP) can shift cystatin C, and with it the estimate, without a true change in kidney filtration.
  • Mayo Clinic Laboratories rejects samples with gross hemolysis or gross icterus (jaundice).
  • The estimate assumes cystatin C is steady from day to day. During acute illness or sudden kidney injury it is unreliable.
  • Labs may use different cystatin C equations (for example CKD-EPI 2012, EKFC, or pediatric equations), and they give different numbers from the same sample.

Reflects current kidney filtration. 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?
  • Could something other than my kidneys be lowering my cystatin C?
  • Should we repeat this test to see whether it stays low for 3 months or more?
  • How does this compare with my creatinine-based eGFR, and would a combined creatinine-plus-cystatin C eGFR be more reliable for me?
  • Could inflammation, my weight, smoking, thyroid or any medicines be affecting my cystatin C?

Questions people ask

Why is my cystatin C eGFR different from my creatinine eGFR?

The two markers are affected by different things. Creatinine depends on muscle mass and diet. Cystatin C is influenced by body fat, smoking, inflammation and thyroid problems. In studies, 25% to 30% of people had estimates that were 15 mL/min/1.73 m² or 20% apart, or more (KDIGO). A big gap is worth asking your clinician about, and a combined creatinine-plus-cystatin C eGFR is usually the most accurate.

Is a cystatin C eGFR better than a creatinine eGFR?

Not in every case. It can be more accurate when creatinine is thrown off by unusual muscle mass, but cystatin C has its own influences. KDIGO says the combined estimate is more accurate than either one alone and recommends it when creatinine alone is less accurate.

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 (cystatin C) unit converter

For clinicians and researchers

The CKD-EPI cystatin C equation (2012, listed by the National Kidney Foundation) is eGFRcys = 133 × min(Scys/0.8, 1)^−0.499 × max(Scys/0.8, 1)^−1.328 × 0.996^age × 0.932 [if female], with Scys in mg/L and age in years. The 2021 CKD-EPI refit produced creatinine-only and creatinine–cystatin C equations without race, and the National Kidney Foundation lists the cystatin C-only equation as the 2012 version. In the 2012 validation set (Inker 2012, 1,119 participants), the median difference between measured and estimated GFR was 3.4 mL/min/1.73 m² for the cystatin C equation, the interquartile range of the difference was 16.4 (13.4 for the combined creatinine–cystatin C equation), and 14.1% of estimates were more than 30% off measured GFR (8.5% for the combined equation). KDIGO 2024 therefore recommends eGFRcr-cys when eGFRcr is less accurate, and reserves eGFRcys alone for specific situations, such as otherwise healthy people with a known change in creatinine generation (for example after limb amputation, with eating disorders, or in bodybuilders). Non-GFR determinants of cystatin C are less well studied than those of creatinine, so KDIGO cautions against assuming eGFRcys is the more accurate estimate in every circumstance. A 2021 meta-analysis found cystatin C higher in hyperthyroidism and lower in hypothyroidism than in controls (Xin 2021), so an overactive thyroid can lower the eGFRcys and an underactive thyroid can raise it. Factors linked to a higher eGFRcr than eGFRcys include older age, higher BMI, weight loss and current smoking, and KDIGO notes that the gap between the two can itself be informative. Some labs and guidelines use other cystatin C equations; KDIGO mentions the EKFC cystatin equation, which has no sex term. Mayo Clinic Laboratories reports a cystatin C eGFR for adults with the CKD-EPI equation and for children with the Schwartz cystatin C equation. KDIGO Table 11 asks labs to report eGFR as a whole number relative to 1.73 m² and flag values below 60 as low. GFR categories are G1 90 or above, G2 60–89, G3a 45–59, G3b 30–44, G4 15–29 and G5 below 15.

LOINC 50210-4 (primary). Specimen: calculated.

Sources

  1. CSTCE - Cystatin C with Estimated Glomerular Filtration Rate (eGFR), Serum, Mayo Clinic Laboratories (via the Schneck Medical Center test catalog)
  2. KDIGO 2024 Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease, Kidney International 105(4S):S117-S314 (2024)
  3. CKD-EPI Cystatin C Equation (2012), National Kidney Foundation
  4. Estimating glomerular filtration rate from serum creatinine and cystatin C, New England Journal of Medicine (2012)
  5. Association Between Serum Cystatin C and Thyroid Diseases: A Systematic Review and Meta-Analysis, Frontiers in Endocrinology (2021)

AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.

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