--- title: "Cystatin C vs creatinine: two ways to estimate kidney function, and when each misleads" type: biomarker-comparison url: "https://www.test-well.com/biomarkers/compare/cystatin-c-vs-creatinine" biomarkers: - Cystatin C - Creatinine reviewed_at: 2026-11-05 review_status: reviewed date_published: 2026-11-04 --- # Cystatin C vs creatinine: two ways to estimate kidney function, and when each misleads > Both are filtered by the kidneys and used to estimate GFR, but they come from different places. Creatinine is a by-product of muscle, so a very muscular person reads 'worse' and a frail or amputee patient reads 'better' than their kidneys deserve, and meat, creatine and some drugs shift it. Cystatin C is made by every nucleated cell at a steady rate and is independent of muscle, but it rises with obesity, thyroid disease, steroids and inflammation. The 2021 race-free equations and the KDIGO 2024 guideline use both together (eGFRcr-cys) for the most accurate estimate, and add cystatin C to confirm or reject a creatinine-based eGFR of 45–59 when there is no other sign of kidney damage. ## Cystatin C vs Creatinine side by side | | Cystatin C | Creatinine | | --- | --- | --- | | What it is | A small protein produced by all nucleated cells at a constant rate, freely filtered and fully broken down by the kidney tubules | A breakdown product of muscle creatine, freely filtered with a small amount secreted by the tubules | | Normal range (adults) | age 18–49: 0.55 – 1 mg/L; age 50+: 0.61 – 1.21 mg/L | Male, age 18+: 0.74 – 1.35 mg/dL; Female, age 18+: 0.59 – 1.04 mg/dL | | What raises it besides kidney function | Obesity, hyperthyroidism, glucocorticoids, smoking, inflammation and some cancers | High muscle mass, a large meat meal or creatine supplements, dehydration, and drugs that block tubular secretion (trimethoprim, cimetidine, some HIV drugs) | | What lowers it falsely | Hypothyroidism; little else | Low muscle mass — older age, frailty, amputation, paralysis, cirrhosis, malnutrition, vegetarian diets | | The eGFR equation | CKD-EPI 2012 cystatin C, or the 2021 combined creatinine–cystatin C equation (the most accurate) | CKD-EPI 2021 creatinine equation, without a race term | | Cost and availability | Less widely run and more expensive; a standard send-out at Quest and Labcorp | On every metabolic panel; the universal first test | | When it is preferred | To confirm CKD when creatinine eGFR is 45–59 without albuminuria; in people with extreme muscle mass or loss; for drug dosing decisions near a threshold | For routine screening and monitoring; trends in the same person are reliable even when the absolute level is biased | ## Why creatinine misleads in some people Creatinine comes from muscle, so the equation that converts it to eGFR assumes an average amount of muscle for your age and sex. A bodybuilder, a heavy meat eater or someone on creatine produces more creatinine and gets an eGFR that looks like early kidney disease; an older, frail, amputee or cirrhotic patient produces less and gets a reassuring eGFR that overstates what the kidneys can do — which matters when drugs are dosed on it. Trimethoprim and cimetidine raise creatinine by blocking its secretion without changing filtration at all. Within one person, creatinine trends are still very useful: the muscle mass does not change week to week, so a rising creatinine is a falling GFR. The bias is in the absolute number, not the direction. ## Where cystatin C has its own blind spots Cystatin C does not depend on muscle, which is its whole advantage, but it is not perfectly steady either. It runs higher with obesity, smoking, an overactive thyroid, systemic glucocorticoids and active inflammation, and lower with an underactive thyroid — so a cystatin C eGFR can understate kidney function in someone on prednisone or with uncontrolled hyperthyroidism. That is why guidelines prefer the two together: the errors are different and partly cancel. ## What the guidelines say: use both The 2021 NKF–ASN task force removed race from the eGFR equations and recommended cystatin C as the way to improve accuracy when it matters; the combined creatinine–cystatin C equation (Inker 2021) is more accurate than either alone and is the one to ask for when a decision hangs on the number. KDIGO 2024 says to measure cystatin C to confirm chronic kidney disease when a creatinine eGFR of 45–59 is the only abnormality — no protein in the urine, no imaging change — because a third of those people have a normal combined eGFR and no CKD. It also recommends it when creatinine is unreliable: very high or very low muscle mass, limb loss, neuromuscular disease, cirrhosis, severe malnutrition, and before dosing drugs with a narrow margin. ## How to read your two results together When both have been measured, the pattern tells you something the single number cannot: - Creatinine eGFR 45–59, cystatin C eGFR above 60 — most likely muscle, diet or a drug rather than kidney disease; the combined eGFR is the number to go by, and if urine albumin is normal, CKD is not diagnosed. - Both below 60 — chronic kidney disease is confirmed; stage it by the combined eGFR and the urine albumin-to-creatinine ratio. - Cystatin C eGFR notably lower than creatinine eGFR — think of obesity, steroids, thyroid disease or inflammation inflating cystatin C, or of low muscle mass flattering the creatinine; a large gap in either direction (more than about 15 mL/min or 30%) also predicts worse outcomes and is worth a nephrology opinion. - Both normal — kidney function is normal; a single measurement of each is enough, and repeat only if risk factors change. ## How do you test Cystatin C and Creatinine? | Test or panel | Type | Price | Fasting | Results | | --- | --- | --- | --- | --- | | [Kidney Health Panel](https://www.test-well.com/tests/kidney-health-panel) | Panel (4 tests) | $64.99 | Yes | 2–4 business days | | [Men's Superpowers Panel](https://www.test-well.com/tests/mens-superpowers-panel) | Panel (36 tests) | $649.99 | Yes | 7–10 business days (most results in 2–5) | | [Total Body Panel](https://www.test-well.com/tests/total-body-panel) | Panel (49 tests) | $599.99 | Yes | 5–10 business days | | [Kidney Function Test (Cystatin C)](https://www.test-well.com/tests/cystatin-c) | Test | $36.99 | No | 2–4 business days | | [Basic Metabolic Panel](https://www.test-well.com/tests/basic-metabolic-panel) | Test | $17.99 | Yes | 1–3 business days | Plus one $6 lab processing fee per order; physician authorization included. ## Common questions ### Is cystatin C better than creatinine? More accurate in people whose muscle mass is far from average, and better at predicting cardiovascular and kidney outcomes in studies — but not a replacement. It has its own biases (obesity, thyroid disease, steroids, inflammation), costs more and is not on routine panels. The most accurate estimate uses both markers together, which is what the 2021 CKD-EPI combined equation and the KDIGO 2024 guideline recommend when the result matters. ### Why is my cystatin C high but my creatinine normal? Either your creatinine is flattering you — low muscle mass from age, frailty, illness, a vegetarian diet or an amputation makes creatinine read normal when GFR is reduced — or something is pushing cystatin C up that is not the kidney: obesity, smoking, hyperthyroidism, prednisone or other steroids, or active inflammation. A combined eGFR, a urine albumin-to-creatinine ratio and a thyroid test usually sort out which; a confirmed low combined eGFR is treated as kidney disease. ### Do I need to fast for a cystatin C or creatinine test? Not for cystatin C. Creatinine is best drawn without a large meat meal in the preceding 12 hours and without a creatine dose that morning, because cooked meat and creatine raise it for several hours; otherwise no fasting is required. Both are usually drawn with the metabolic panel, so the fasting rules of that panel apply if glucose is being measured. ### What is eGFR cystatin C? An estimate of glomerular filtration rate calculated from the cystatin C level, age and sex using the CKD-EPI 2012 equation — the cystatin C equivalent of the creatinine-based eGFR on a metabolic panel. A combined eGFR (eGFRcr-cys) uses both markers in one equation and is the most accurate of the three. All are reported in mL/min/1.73 m², with 60 and 45 the usual decision thresholds. ## Related - [Cystatin C: reference range and what high or low means](https://www.test-well.com/biomarkers/cystatin-c) - [Creatinine: reference range and what high or low means](https://www.test-well.com/biomarkers/creatinine) - [Lab results explainer](https://www.test-well.com/tools/lab-results-explainer) ## Sources - [Inker et al., New Creatinine- and Cystatin C–Based Equations to Estimate GFR without Race (NEJM 2021)](https://doi.org/10.1056/NEJMoa2102953) - [Delgado et al., A Unifying Approach for GFR Estimation: Recommendations of the NKF-ASN Task Force on Reassessing the Inclusion of Race in Diagnosing Kidney Disease (American Journal of Kidney Diseases 2022)](https://doi.org/10.1053/j.ajkd.2021.08.003) - [KDIGO 2024 Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease](https://kdigo.org/guidelines/ckd-evaluation-and-management/) - [Mayo Clinic Labs](https://www.mayocliniclabs.com/test-catalog/overview/65653) - [Testing.com (AACC) — Cystatin C Test: What It Measures and How It Works](https://www.testing.com/tests/cystatin-c/) - [MedlinePlus (NIH) — Creatinine Test](https://medlineplus.gov/lab-tests/creatinine-test/) --- Medically reviewed by Youmna DiStefano, MD (Medical Reviewer, TestWell); last reviewed 2026-11-05. Review policy: https://www.test-well.com/reviewers/youmna-distefano-md Canonical page: https://www.test-well.com/biomarkers/compare/cystatin-c-vs-creatinine Machine-readable catalog: https://www.test-well.com/api/catalog.json · MCP server: https://www.test-well.com/mcp · Overview for agents: https://www.test-well.com/llms.txt Prices are cash-pay, in USD, and include physician authorization; every order adds one flat $6 lab processing fee. Educational content is not a diagnosis — discuss results with a clinician.