Cystatin C blood test
In short
A typical adult cystatin C result is 0.63 to 1.03 mg/L (age 18–49) and 0.67 to 1.21 mg/L (age 50+). A high cystatin C most often means the kidneys are filtering less than expected. Doctors read it with creatinine to get the most accurate eGFR. Always read your result against the range printed on your own report.
A small protein that shows how well the kidneys filter.
Every cell in your body makes cystatin C at a steady rate, and healthy kidneys clear it. Unlike creatinine, it is hardly affected by muscle or diet. Doctors often use it to double-check a borderline eGFR, the usual kidney estimate.
Is my Cystatin C high or low?
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Typical range
| For | Range | Unit |
|---|---|---|
| Adults · age 18–49 | 0.63–1.03 | mg/L |
| Adults · age 50+ | 0.67–1.21 | mg/L |
Typical ranges for adults. Labs differ a little, so the range printed next to your result is the one to go by.
If your Cystatin C is high
A high cystatin C most often means the kidneys are filtering less than expected. Doctors read it with creatinine to get the most accurate eGFR.
Common reasons
- Older age, as kidney filtering slowly falls
- Steroid medicines
- An overactive thyroid
- Inflammation, smoking or extra body weight
- Kidneys filtering less, often with diabetes or high blood pressure
- Less often: a sudden kidney injury or another kidney condition
If your Cystatin C is low
A low cystatin C is rarely a concern. It usually means the kidneys are filtering well.
Common reasons
- Kidneys that filter well
- An underactive thyroid
- Natural variation between people
What can throw it off
Thyroid problems, steroid medicines and inflammation can shift cystatin C apart from the kidneys.
Questions to take to your appointment
- 1Does my eGFR look different when cystatin C is used?
- 2Could my thyroid or medicines be affecting it?
Read together with
Doctors rarely read Cystatin C alone. These usually sit next to it.
Quick answers
What is the cystatin C blood test?
Cystatin C: A small protein that shows how well the kidneys filter. Every cell in your body makes cystatin C at a steady rate, and healthy kidneys clear it. Unlike creatinine, it is hardly affected by muscle or diet. Doctors often use it to double-check a borderline eGFR, the usual kidney estimate.
What is a normal cystatin C level?
For most adults, cystatin C is typically 0.63 to 1.03 mg/L (age 18–49) and 0.67 to 1.21 mg/L (age 50+). Labs differ a little, so the range printed next to your result is the one to go by.
What does a high cystatin C mean?
A high cystatin C most often means the kidneys are filtering less than expected. Doctors read it with creatinine to get the most accurate eGFR. Common reasons include older age, as kidney filtering slowly falls; steroid medicines; an overactive thyroid; and inflammation, smoking or extra body weight. A doctor reads it together with your other results and how you feel.
What does a low cystatin C mean?
A low cystatin C is rarely a concern. It usually means the kidneys are filtering well. Common reasons include kidneys that filter well; an underactive thyroid; and natural variation between people.
What can affect my cystatin C result?
Thyroid problems, steroid medicines and inflammation can shift cystatin C apart from the kidneys.
What should I ask my doctor about my cystatin C?
Questions worth taking to the appointment: Does my eGFR look different when cystatin C is used? Could my thyroid or medicines be affecting it?
What this page can’t do
It reads each number on its own.
Doctors read results together — ALT with AST, ferritin with hemoglobin, TSH with free T4. A pattern says more than any single flag.
It doesn't know you.
Your age, your medicines, how you feel and your last result all change what a number means.
It doesn't remember.
Close this page and your results are gone. That's on purpose: nothing was ever sent to us.
We also make Vita: Health Coach, an app for those parts. It reads your whole report with your medicines and history in mind, answers follow-up questions in plain words, and keeps your reports in one place — for you and for the people you look after.
Vita: Health Coach on the App StoreSources
- Mayo Clinic Laboratories — Cystatin C with eGFR, serum
- Updated reference intervals for serum cystatin C and creatinine (PMC)
- Non-renal factors that affect cystatin C (PMC)
Stuck on a word? See the medical words. How we choose our sources. More about Vita Health Coach.