Cystatin C
cystatin C test · kidney function test · cystatin C eGFR
This blood test checks a protein that shows how well your kidneys clean your blood.
When kidney function needs a more precise check, especially if creatinine may be misleading: in older people, in people with a lot of muscle or very little, and before choosing medicine doses.
⏱ Duration: the blood draw usually takes 5 minutes; results usually come in 1 to 3 days
Be sure to tell your doctor
How to prepare
- Food. You usually do not need to fast, but it is often done with other blood chemistry tests that need fasting. Check with the lab.
- Medicines. Do not stop anything on your own. Tell your doctor what you take.
What to bring
- Your referral
- Past creatinine results
How it goes
- You sit down, and a band is tied above your elbow
- The skin is wiped with antiseptic
- Blood is taken from a vein into a tube
- The band is removed, and a cotton pad is pressed on the spot
What you'll feel
- A quick prick, like a pinch
- Sometimes slight dizziness. Tell the nurse, and they will help you lie down
Afterwards
- Press the cotton pad for 3 to 5 minutes
- Results usually come in 1 to 3 days
- The doctor will use it to work out your kidney function and adjust medicine doses if needed
Common questions
Why cystatin C if I already have creatinine?
Creatinine depends on your muscles and diet. Cystatin C depends on them less, so together they give a more accurate picture.
Do I need to fast?
Cystatin C itself barely depends on food. But if you also have chemistry tests, fasting is better. Check with the lab.