# Cystatin C: Kidney filtration marker less affected by muscle mass than creatinine

> Cystatin C checks your kidneys without the muscle and diet effects that skew creatinine. Check your result, and see when the test is worth it.

- Also called Serum cystatin C and Cys C
- Not on a standard checkup
- Fasting preferred
- Web page: https://picardo.health/guides/biomarkers/cystatin-c

## The short answer

Cystatin C is a small protein your kidneys filter out of your blood. Unlike creatinine, it barely depends on your muscle or diet, so it can confirm a kidney result creatinine might have gotten wrong. Labcorp’s range is 0.60 to 1.00 mg/L up to age 50.[1][2][3]

- **A good result:** Up to 1.00 mg/L if you’re 50 or under. The upper limit is higher later in life, such as 1.16 on a report for a 62-year-old woman.[3][4]
- **If yours is high:** Look at the eGFR beside it. Under 60 needs a repeat test and a urine albumin test. Combined with your creatinine, it gives the most accurate estimate.[1][6]
- **Should you test?** When creatinine may mislead, such as with a lot of muscle or very little, creatine supplements or a borderline eGFR that would change a decision.[1][7]

## What is a normal cystatin C level?

Labcorp’s range is 0.60 to 1.00 mg/L up to age 50, and its upper limit rises after that.[3][4] Your report also turns cystatin C into an eGFR, which accounts for your age and sex:[2]

| Result (mg/L) | What it means |
| --- | --- |
| Under 1.01 | Not raised |
| 1.01 to 1.38 | Above the range for some ages |
| 1.39 to 2.33 | High enough to mean an eGFR under 60 |
| 2.34 or more | High enough to mean an eGFR under 30 |

### Not raised

**Range:** 1.00 mg/L or less.

Your cystatin C isn’t above Labcorp’s upper limit of 1.00, which applies up to age 50, and older adults have a higher limit.[3][4] The eGFR on your report shows what it means for your kidneys.[2]

**How worried to be:** Nothing to worry about.

**What to do next:**

1. If your creatinine eGFR was low but this one is normal, muscle or diet may have been skewing your creatinine. Combining the two gives the most accurate estimate.[1][6]
2. If you have high blood pressure or diabetes, check your urine albumin too. It finds kidney damage that cystatin C misses.[1]

### Above the range for some ages

**Range:** 1.01 to 1.38 mg/L.

Labcorp flags anything over 1.00 up to age 50, and allows up to 1.16 on a report for a 62-year-old woman.[3][4] Your age and sex decide what it means: at 1.2 mg/L, the equation gives an eGFR of about 69 for a 30-year-old man and about 55 for a 70-year-old woman.[5]

**How worried to be:** Not urgent. Check the eGFR on your report.

**What to do next:**

1. If the eGFR is under 60, repeat it with a creatinine test and a urine albumin test.[1]
2. A clinician can combine your cystatin C and creatinine into one eGFR, the most accurate estimate.[1][6]

[Test Urine albumin and a metabolic panel, $14.50](https://app.picardo.health/labs/order?tests=140285,322000&ref=guide-cystatin-c)

### High enough to mean an eGFR under 60

**Range:** 1.39 to 2.33 mg/L.

At this level, the cystatin C equation gives an eGFR under 60 at any adult age, and at older ages it may already be under 30.[5] If it lasts three months or more, and an eGFR combining it with creatinine agrees, that’s chronic kidney disease. Muscle and diet don’t explain it, though steroid medicines such as prednisone, smoking, extra body fat and inflammation are thought to raise cystatin C, and thyroid problems can shift it.[1]

**How worried to be:** Worth seeing a clinician in the next few weeks. Sooner if your eGFR is under 30.

**What to do next:**

1. Repeat it with a creatinine test and a urine albumin test.[1]
2. Ask a clinician about blood pressure, medicines that protect your kidneys and, if you’re 50 or older, a statin.[1]

[Test Urine albumin and a metabolic panel, $14.50](https://app.picardo.health/labs/order?tests=140285,322000&ref=guide-cystatin-c)

### High enough to mean an eGFR under 30

**Range:** 2.34 mg/L or more.

At this level, the cystatin C equation gives an eGFR under 30 at any adult age, which is severely reduced kidney function.[5] KDIGO advises care from a kidney specialist below 30.[1]

**How worried to be:** If this is new or you feel unwell, contact a clinician today. Otherwise, within days.

**What to do next:**

1. If you didn’t know about a kidney problem, get seen promptly. It may be a sudden kidney injury.[1]
2. Ask for a referral to a kidney specialist (nephrologist).[1]
3. If you already see one, share the result with them.

## What is cystatin C?

> Think of creatinine and cystatin C as two witnesses to how well your kidneys work. Creatinine’s story depends on your muscles and your last meal; cystatin C’s mostly doesn’t. When they agree, you can trust them. When they don’t, it’s worth finding out why.

Your kidneys clear cystatin C from your blood, so it builds up when they filter less. Its level barely depends on muscle or diet, which is the main weakness of creatinine.[1][2]

Like creatinine, it’s turned into an eGFR. Labcorp uses the 2012 CKD-EPI cystatin C equation, which accounts for age and sex.[2][5] On its own it’s no more accurate than creatinine overall. Its strength is having different blind spots.[6]

## Is cystatin C better than creatinine?

Each has its own blind spots, so the best estimate uses both.[1][6]

|  | Creatinine | Cystatin C |
| --- | --- | --- |
| Depends on muscle and diet | A lot | Barely |
| Also changed by | Muscle, meat, creatine and some medicines | Steroid medicines, thyroid problems, smoking, body fat and inflammation |
| On a standard checkup | Yes | No |
| eGFR within 30% of a measured GFR | About 87% of the time | About 85% to 89% alone; about 91% combined with creatinine |

Accuracy from the study behind the 2021 equations.[6] Other factors from KDIGO 2024.[1]

KDIGO recommends the combined estimate when creatinine may be misleading and the result affects decisions, and for staging kidney disease wherever cystatin C is available.[1] Since 2021, US kidney societies have called for routine use, especially to confirm eGFR in adults who have, or are at risk of, kidney disease.[7]

## What does it mean when the two disagree?

Cystatin C often gives a lower eGFR than creatinine, and the gap grows with age.[8] In a 2025 analysis of 821,327 outpatients, 11% had a cystatin C eGFR at least 30% lower than their creatinine eGFR.[8]

Over about 11 years, those people had 1.69 times the risk of death, 1.54 times the risk of heart failure and 1.29 times the risk of kidney failure of people whose two results agreed.[8] That’s a link rather than proof that the gap causes harm. But it suggests the lower number deserves attention.

## How to lower cystatin C

There’s no way to lower cystatin C directly. It falls when its cause improves:

- **Treating kidney disease:** If your kidneys filter less, an SGLT2 inhibitor, an ACE inhibitor or ARB and lower blood pressure slow the decline. The eGFR page covers who they suit.[1] How much it helps: a little. How sure we are: very sure.
- **Treating a non-kidney cause:** Steroid medicines such as prednisone and inflammation are thought to raise cystatin C on their own, and thyroid problems can shift it.[1] How much it helps: some. How sure we are: early evidence.
- **Stopping smoking:** Smoking is linked to higher cystatin C, and KDIGO advises people with kidney disease to stop.[1] How much it helps: a little. How sure we are: early evidence.

## Who should get a cystatin C test?

It isn’t used to screen everyone. KDIGO recommends it when creatinine may mislead:[1]

- You have a lot of muscle, or very little, from age, illness, an amputation or an eating disorder.
- You eat a very high-protein, keto or vegetarian diet, or take creatine.
- You take anabolic steroids or testosterone, or medicines that block how your kidneys clear creatinine.
- Your eGFR is near a cutoff that would change a diagnosis or a medicine dose.

US kidney societies also advise using it routinely to confirm eGFR in adults who have, or are at risk of, kidney disease.[7]

## How to get a cystatin C test, and what it costs

It comes from the cystatin C test, which costs $47.25 through Picardo.

- [Cystatin C test, $47.25](https://app.picardo.health/labs/order?tests=121265&ref=guide-cystatin-c). The test this number comes from. Labcorp 121265, fasting preferred.

Every order comes with:

- Results in 2 to 3 days, in the app
- Physician follow-up if you want one
- Free Labcorp draw, or $75 at home
- No other fees. HSA and FSA eligible.

Already have a result? [Ask Picardo about it](https://app.picardo.health/auth).

## Questions people ask

### Should I check cystatin C if my eGFR is just under 60?

It’s one of the best times to. Whether you’re told you have kidney disease can hang on that one number, and US kidney societies advise cystatin C to confirm eGFR in adults who have, or are at risk of, kidney disease.[1][7]

### Why is my cystatin C eGFR lower than my creatinine eGFR?

It’s common, especially as people age.[8] Smoking, extra body fat, steroid medicines such as prednisone and inflammation are thought to push cystatin C up, and low muscle pushes creatinine down.[1] Large gaps still matter, though. People with them had higher risks of heart failure and death in a 2025 analysis.[8]

### Does creatine affect cystatin C?

Not the way it affects creatinine. Creatine supplements raise creatinine, which is one of the reasons KDIGO gives for checking cystatin C instead.[1]

### Do I need to fast for a cystatin C test?

Labcorp prefers an overnight fast.[2] If the same draw includes a metabolic panel, fast for 12 hours.

### Can weight-loss drugs change cystatin C?

Possibly. A draft KDIGO update, out for comment in October 2026, warns that in people with kidney disease, both creatinine and cystatin C can mislead while body composition changes on GLP-1 drugs such as semaglutide.[9]

## Often checked alongside

- [eGFR](https://picardo.health/guides/biomarkers/egfr.md): How well your kidneys filter
- [Creatinine](https://picardo.health/guides/biomarkers/creatinine.md): Muscle waste the kidneys filter out
- [Urine albumin-to-creatinine ratio](https://picardo.health/guides/biomarkers/urine-albumin-creatinine-ratio.md): Early kidney damage, from a urine sample
- [BUN](https://picardo.health/guides/biomarkers/bun.md): Protein waste the kidneys clear

## Test details

- **Labcorp test:** Cystatin C With Glomerular Filtration Rate, Estimated (eGFR), 121265
- **LOINC:** 33863-2
- **Sample:** Blood
- **Fasting:** Overnight fasting preferred[2]
- **Typical lab range:** 0.60 to 1.00 mg/L up to age 50;[3] higher after that, such as 0.72 to 1.16 mg/L for a 62-year-old woman[4]
- **Equation:** CKD-EPI 2012 cystatin C, reported as an eGFR in mL/min/1.73 m²[2][5]
- **Units:** mg/L

## Sources

1. Kidney Disease: Improving Global Outcomes (KDIGO) CKD Work Group. KDIGO 2024 clinical practice guideline for the evaluation and management of chronic kidney disease. Kidney Int. 2024;105(4S):S117–S314. https://doi.org/10.1016/j.kint.2023.10.018
2. Labcorp. Cystatin C with glomerular filtration rate, estimated (eGFR), test 121265. Labcorp test menu. Accessed October 28, 2026. https://www.labcorp.com/tests/121265/cystatin-c-with-glomerular-filtration-rate-estimated-egfr
3. Labcorp. Pediatric testing reference ranges. Burlington, NC; 2022. https://www.labcorp.com/content/dam/labcorp/drupal/178250_DX_TL_PediatricTestRef_Final.pdf
4. Labcorp. eGFR creatinine-cystatin C calculation with albumin:creatinine-protein:creatinine ratios, urine, test 121065. Sample report, collected August 1, 2022. Accessed October 28, 2026. https://files.labcorp.com/testmenu-d8/sample_reports/121065.pdf
5. Inker LA, Schmid CH, Tighiouart H, et al. Estimating glomerular filtration rate from serum creatinine and cystatin C. N Engl J Med. 2012;367(1):20–29. https://doi.org/10.1056/NEJMoa1114248
6. Inker LA, Eneanya ND, Coresh J, et al. New creatinine- and cystatin C–based equations to estimate GFR without race. N Engl J Med. 2021;385(19):1737–1749. https://doi.org/10.1056/NEJMoa2102953
7. Delgado C, Baweja M, Crews DC, 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. J Am Soc Nephrol. 2021;32(12):2994–3015. https://doi.org/10.1681/ASN.2021070988
8. Estrella MM, Ballew SH, Sang Y, et al. Discordance in creatinine- and cystatin C-based eGFR and clinical outcomes: a meta-analysis. JAMA. 2025;334(21):1915–1926. https://doi.org/10.1001/jama.2025.17578
9. Kidney Disease: Improving Global Outcomes (KDIGO). KDIGO 2027 clinical practice guideline for the evaluation and management of chronic kidney disease (CKD): medications management. Public review draft. October 2026. https://kdigo.org/wp-content/uploads/2026/10/KDIGO-2027-CKD-Guideline-Focused-Update-Public-Review-Draft.pdf

Updated 2026-11-04. This is general health information, not medical advice: talk to your clinician about your results and before changing any treatment.