Cystatin C is a small protein that all body cells produce at a steady rate and the kidneys fully filter. It is a modern, accurate marker of kidney function.
Its main advantage over creatinine: cystatin C hardly depends on muscle mass, sex or diet. So in the elderly, in athletes and in people of non-standard build it estimates GFR more reliably.
Reference ranges
Approximate reference for adults:
| Adults | 0.5 – 1.0 mg/L |
| Advantage | independent of muscle and diet |
| Use | to calculate eGFR from cystatin C |
What an elevated level means
A high cystatin C means a decline in the kidneys' filtration function — and, unlike creatinine, this now depends little on muscle or diet, so the signal is "cleaner".
The causes are the same as for a reduced eGFR: chronic kidney disease, diabetic and hypertensive nephropathy, acute kidney injury.
The level is slightly affected by thyroid function, inflammation and high-dose corticosteroids.
What a low level means
A low cystatin C is a favorable sign of good kidney filtration and usually needs no attention.
How the test is done
Venous blood. It needs no special preparation — another way in which it is more convenient than creatinine, which is affected by meat and workouts.
Cystatin C is especially useful when the "creatinine" eGFR is in doubt: in the elderly, in athletes, and with very low or very high muscle mass.
What affects the value
- Kidney function — the main and almost the only significant factor.
- Age — the level rises slightly over the years.
- Thyroid gland — marked disorders have a small effect.
- High-dose corticosteroids — can raise it.
- Muscle mass — unlike creatinine, its effect is minimal.
Calculate using this marker
Calculators where Cystatin C is used directly:
Frequently asked questions
Is cystatin C better than creatinine?
In many cases — yes, it estimates GFR more accurately because it does not depend on muscle mass, sex or diet. It is especially useful in the elderly, in athletes and in people of non-standard build, where creatinine is deceptive. They are often used together.
Is any preparation needed for the test?
Practically none — unlike creatinine, cystatin C is not affected by a meat meal or workouts. A venous blood draw is enough.
When should cystatin C be tested?
When the creatinine-based eGFR is in doubt: in the elderly, in people with very high or very low muscle mass, in athletes, and for a more accurate assessment of kidney function over time.