What is cystatin C?
Cystatin C is a small protein that almost every cell in your body makes at a fairly constant rate. It inhibits certain enzymes, but that is not why it is measured. It is measured because your kidneys filter it almost completely out of the blood and break it down: if the kidneys filter less, it accumulates. The amount in your blood is therefore a mirror of your filtration. Creatinine does the same in principle, but creatinine comes from muscle. Anyone with a lot of muscle mass, a strength athlete or a large man, makes more creatinine and therefore appears to have worse kidney function than they have. Anyone with little muscle, a slight or older woman, someone who lost a lot of weight, makes little and gets an estimate that is too rosy. Cystatin C does not have that problem, and that is the whole reason it exists. Your report shows cystatin C in mg/L, often with an eGFR beside it calculated from it. The range rises with age, because kidney function declines slowly from your thirties; one lab builds that into age bands, from about 0.60 to 1.03 mg/L in a man of thirty to 0.82 to 1.53 mg/L over seventy, where the other uses one range of 0.62 to 1.11 mg/L for all adults.
Why is cystatin C relevant?
Your kidneys are silent workers: they filter some 180 litres of blood a day, and you only notice something once a large part of their capacity is gone. A kidney function that declines slowly, from years of high blood pressure, high blood sugar or excess weight, gives no symptoms until it is far along. That is why a kidney value is on almost every report, and why it matters that the value is right. That is exactly where cystatin C earns its place for anyone who wants to stay healthy and exercises a lot. A strength athlete with a high creatinine gets an eGFR that looks too low, and a second measurement on cystatin C removes the worry. Conversely, someone with little muscle can have a normal creatinine while the kidneys are already giving ground; cystatin C does show that. In general practice it is used for that reason when the eGFR from creatinine cannot be trusted, and to confirm or dismiss a suspicion of kidney damage. The best estimate comes from both together. Where the two agree, they confirm each other; where they diverge, the gap itself is the information, and it almost always points at muscle mass or at one of the other things that move cystatin C itself. Because cystatin C is not entirely independent of who you are either. An overactive thyroid, prednisone, smoking, excess weight and inflammation raise it a little without the kidneys changing; an underactive thyroid lowers it. Small effects, but worth knowing when the two estimates diverge.
What Dutch labs actually use
The contrast between the two laboratories is the finding here. Unilabs publishes one band for all adults, 0.62 to 1.11 mg/l. Star-shl bands by sex and by decade, from 0.60 to 1.03 in a man of thirty to 0.82 to 1.53 in a man over seventy. A man of 72 with 1.3 mg/l is raised at Unilabs and inside his own age band at Star-shl. That matters especially for this test, because cystatin C is recommended for not moving with muscle mass, while by this table it clearly does move with age.
0.62 – 0.98mg/L
Between 0.59 and 0.62 and between 0.98 and 1.11 it depends on the lab, because each sets its limits on its own method and population. Above 1.11 every lab calls it abnormal.
every lab calls 0.62 – 0.98 mg/L normal. Between 0.59 and 0.62 and between 0.98 and 1.11 it depends on the lab.
Every age, per lab
| Laboratory | Group | Reference range |
|---|---|---|
| Unilabs(Saltro, Medlon, SHO, Atalmedial)2026 | Alle leeftijden | 0,62-1,11 mg/L |
| Star-shl2026 | Man 23 t/m 30 jaar | 0,60-1,03 mg/L |
| Vrouw 23 t/m 30 jaar | 0,57-0,90 mg/L | |
| Man 30 t/m 40 jaar | 0,64-1,12 mg/L | |
| Vrouw 30 t/m 40 jaar | 0,59-0,98 mg/L | |
| Man 40 t/m 50 jaar | 0,68-1,22 mg/L | |
| Vrouw 40 t/m 50 jaar | 0,62-1,07 mg/L | |
| Man 50 t/m 60 jaar | 0,72-1,32 mg/L | |
| Vrouw 50 t/m 60 jaar | 0,64-1,17 mg/L | |
| Man 60 t/m 70 jaar | 0,77-1,42 mg/L | |
| Vrouw 60 t/m 70 jaar | 0,66-1,26 mg/L | |
| Man boven 70 jaar | 0,82-1,53 mg/L | |
| Vrouw boven 70 jaar | 0,68-1,36 mg/L |
Each band as the lab publishes it, retrieved in 2026, unless marked otherwise.
Cystatin C high or low: what it means
A high cystatin C means, first of all, less filtration, and the usual causes of that are the familiar ones: years of high blood pressure, diabetes, excess weight, smoking, and age itself, because from your thirties filtration declines slowly. It rises temporarily with dehydration and with medicines that burden the kidneys, such as anti-inflammatory painkillers like ibuprofen and naproxen. And without the kidneys changing: an overactive thyroid, prednisone, smoking and excess weight. A low cystatin C is favourable: your kidneys filter briskly and little stays behind. A deficiency of cystatin C does not exist. Occasionally a low value is an underactive thyroid, which slows production; TSH shows that. Protecting your kidney function is what protects your blood pressure, blood sugar and weight: losing weight around the middle, daily movement, little salt, not smoking and drinking enough. Anti-inflammatory painkillers such as ibuprofen and naproxen are the medicines that most often burden healthy kidneys; use them briefly and not when you are dehydrated. Anyone who already has kidney damage can slow the decline but not reverse it, and then blood pressure and blood sugar are the two that count most. Read cystatin C beside creatinine and the eGFR from both, and beside protein in the urine, which shows damage earlier than filtration does. When comparing over time, keep to one and the same lab, because one compares your value with your age group and the other with all adults.
What lowers it
Brisk filtration, and very occasionally the thyroid.
| Cause | How often |
|---|---|
| A generous filtration rateWhat the kidney filters out does not stay behind in the blood; the ordinary outcome with healthy kidneys and at a young age | Often |
| Underactive thyroidA low thyroid function slows the production of cystatin C a little, making kidney function look better than it is; TSH shows it | Rare |
What raises it
Less filtration, age, and a few things that raise production itself.
| Cause | How often |
|---|---|
| Reduced kidney functionThe reason this value is measured: years of high blood pressure, diabetes or excess weight, and temporarily dehydration or anti-inflammatory painkillers like ibuprofen | Often |
| AgeFiltration declines slowly from your thirties, and the range therefore rises by decade | Often |
| Overactive thyroid, prednisone, smoking or excess weightRaise the production of cystatin C a little without the kidneys changing; a small effect, but it sometimes explains a gap with creatinine | Sometimes |
How does a cystatin C blood test work?
- Referral
- Not needed. You can have cystatin C measured without going through your GP.
- Fasting
- Not needed. Drink normally, because dehydration lifts every kidney value temporarily.
- The draw
- One tube of blood from a vein in your arm, ideally together with creatinine from the same draw.
- The result
- A single number in mg/L, often with an eGFR beside it calculated from it. One lab compares your value with your age group, the other with all adults.
- Repeating
- With an unexpectedly high value: again after a few weeks, well hydrated and without anti-inflammatory painkillers, together with creatinine and protein in the urine. With healthy kidneys a yearly measurement is enough.
- Where to draw
- You can draw at 250+ locations near you, no referral needed. See the locations
Frequently asked questions
What is cystatin C?
Cystatin C is a small protein all your cells release at a steady rate. Your kidneys filter it out of your blood, like creatinine, so the more of it stays behind, the less is being filtered. The difference with creatinine is that it does not come from muscle tissue: your muscle mass does not affect the value. That is why it is useful where creatinine distorts.
What is a normal cystatin C level?
That depends on your lab and your age. One lab uses 0.62 to 1.11 mg/L for all adults; the other works with bands by sex and by decade, from 0.60 to 1.03 mg/L in a man of thirty to 0.82 to 1.53 mg/L over seventy, because filtration declines with the years. Lower is more favourable. Compare your value with the range printed beside it, and with the eGFR calculated from it.
What does a high cystatin C mean?
First of all that your kidneys filter less, usually from years of high blood pressure, high blood sugar or excess weight, or simply from age. The value rises temporarily with dehydration and with anti-inflammatory painkillers like ibuprofen. And a few things raise production itself, without the kidneys changing: an overactive thyroid, prednisone, smoking and excess weight. So read the value beside creatinine and protein in the urine.
What does a low cystatin C mean?
That your kidneys filter briskly, and that is favourable; a deficiency of cystatin C does not exist. Occasionally a low value is the result of an underactive thyroid, which slows production and thereby makes kidney function look better than it is.
Why cystatin C beside creatinine?
Because creatinine comes from muscle tissue. Anyone with a lot of muscle therefore appears to have worse kidney function than they have; anyone with little muscle, better. Cystatin C comes from all cells and does not have that problem. The best estimate comes from the two together, and where they diverge, the gap itself is the information.
I exercise a lot and my creatinine is high; does cystatin C say more?
Yes, this is exactly the situation it exists for. A lot of muscle mass and protein-rich eating lift creatinine and push the eGFR down, while the kidneys work perfectly well. A cystatin C within range, with a normal eGFR from it, shows that and removes the worry. If cystatin C rises with it, it is about filtration after all.
How do I keep my kidneys healthy?
With what keeps your blood pressure, blood sugar and weight healthy: losing weight around the middle, daily movement, little salt, not smoking and drinking enough. Use anti-inflammatory painkillers such as ibuprofen and naproxen briefly and not when you are dehydrated, because those are the medicines that most often burden healthy kidneys. With years of high blood pressure or diabetes, a yearly kidney value is the way to catch a slow decline in time.
Do I need to fast?
No. Do drink normally, because dehydration lifts every kidney value temporarily, and have creatinine measured from the same draw, because the two are read together.
Which tests include cystatin C?
Cystatin C is part of Advanced, the broader panel. It is not orderable yet.
Related biomarkers
Sources
- 1.NHG guideline on chronic kidney disease (M109), Dutch College of General Practitioners. 2026. richtlijnen.nhg.org
- 2.Unilabs, Bepalingenklapper: cystatine C. 2026. bepalingenklapper.nl
- 3.Star-shl, Labbepalingen: cystatine C. 2026. star-shl.nl
Educational information only, not medical advice. Consult a healthcare professional for clinical decisions.
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Cystatin C is part of Advanced, the broader panel. It is not orderable yet.
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