Cystatin C, Serum
This test measures the level of cystatin C, a protein produced by all cells in your body. It helps assess kidney function.
["Cystatin C is a useful marker for checking how well your kidneys are working."]
Key facts at a glance
- LOINC
- 43581-8
- Short code
- C4PF
- Synonyms
- C4 Prt-mCnc
- Category
- chemistry
- Sample
- serum
- Container
- Sterile, screw-capped, leak-proof container; sterile vacutainer tube without anticoagulant preferred.
- Units
- N/A
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- ≥ 18 years
- Method
- Immunonephelometry
- CPT
- 86160
- SNOMED
- 444097001
- Specimen volume
- 1-5 mL of peritoneal fluid
- Stability
- Ambient: 2 hours; Refrigerated (2-8°C): 24 hours; Frozen (-20°C or below): 1 month. Avoid repeated freeze-thaw cycles.
- Hemolysis max
- 500
- Lipemia max
- 1000
- Icterus max
- 500
- TAT
- 4–24 hours
- Order
- routine
Why Is This Test Done?
Your doctor may order this test to evaluate kidney health, especially if you have symptoms like fatigue, swelling, or changes in urine output. It’s also useful for monitoring kidney disease progression or response to treatment. Cystatin C is often used alongside other tests, like creatinine, to get a clearer picture of kidney function.
What to Expect Before the Test
No special preparation is needed for this blood test. You may have a small needle inserted into your arm to draw blood. If you’re on blood thinners or have a history of bleeding issues, let your doctor know beforehand.
What the Results Mean
Higher than expected levels of cystatin C may indicate kidney problems, while lower levels could suggest overhydration or other conditions. Your doctor will compare your results to your medical history and other tests to interpret them accurately.
Common Causes of Abnormal Results
Elevated cystatin C levels can be linked to kidney disease, dehydration, or certain medications. Lower levels might be seen in overhydration or conditions affecting protein production. Always discuss results with your healthcare provider.
Reference range
Reference ranges for complement C4 in peritoneal fluid are not well established; results should be interpreted in conjunction with serum C4 levels and clinical context. Peritoneal fluid C4 is typically evaluated as a ratio to serum C4 or albumin to determine selective transudation versus exudation.N/A
No special patient preparation required. Specimen is typically collected during paracentesis procedure for clinical evaluation of ascites.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
◆Associated findings1
Short name
Cystatin C
Frequently asked questions
How often do I need this test?
Can diet or exercise affect cystatin C levels?
Is this test the same as a creatinine test?
Sources
- 1
- 2Lab Tests OnlineSource
- 3
Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.
This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.
This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.
If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.
Medically reviewed by WellAlly Editorial Team Last reviewed August 16, 2026. · Read our editorial policy