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Serum Creatinine with Glomerular Filtration Rate (GFR) Estimation (Cystatin C-based)

Published: August 9, 2026Updated: August 16, 2026

This test measures your kidney function by analyzing a protein called cystatin C in your blood. It helps determine how well your kidneys are filtering waste from your blood.

Quick summary

["A cystatin C GFR test helps assess kidney health and risk of kidney disease or damage."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 16, 2026Editorial policy

Key facts at a glance

LOINC
25285-8
Short code
S pneum Da 18C IgG 2:1 Ser-Rto
Synonyms
S pneum Da 18C IgG 2:1 Ser-Rto
Category
coagulation
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
CPT
82784
Specimen volume
5 mL
Stability
Room temperature: 4h, Refrigerated: 24h, Frozen: 7d
Hemolysis max
500
Lipemia max
1000
Icterus max
500
TAT
4–24 hours
Order
routine

Why This Test Matters

Kidneys play a vital role in filtering waste and excess fluids from your blood. This test uses cystatin C, a protein produced by all cells in your body, to estimate how well your kidneys are working. Unlike traditional creatinine-based GFR tests, cystatin C provides a more accurate reflection of kidney function, especially in people with lower muscle mass or certain medical conditions.

How the Test Works

Your blood sample is sent to a lab where cystatin C levels are measured using a specialized immunoassay technique. The lab then calculates your estimated glomerular filtration rate (GFR) based on your cystatin C level and other factors like age, sex, and race.

Preparation for the Test

No special preparation is needed for this test. You can eat and drink normally on the day of your blood draw. However, inform your healthcare provider about any medications you’re taking, as some may affect kidney function.

What to Expect During the Test

A healthcare professional will insert a small needle into a vein in your arm to draw blood. The process usually takes a few minutes. You may feel a brief pinch or slight discomfort, but it’s generally well-tolerated. Afterward, you can resume your normal activities.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Cystatin C GFR

Frequently asked questions

What does a cystatin C GFR test tell your doctor?
This test helps identify early signs of kidney disease, even before symptoms appear. Low GFR levels may indicate impaired kidney function, which can lead to serious health issues like high blood pressure, heart disease, or anemia. It’s particularly useful for monitoring kidney health in people with diabetes, hypertension, or a family history of kidney problems.
How often should I get this test?
Your doctor will determine how often you need this test based on your overall health, medical history, and any risk factors for kidney disease. Typically, it may be recommended annually or more frequently if you have conditions like diabetes or chronic kidney disease.
Can diet or medications affect cystatin C levels?
Dietary changes alone rarely affect cystatin C levels, but certain medications—such as some antibiotics, pain relievers, or medications for high blood pressure—may influence kidney function indirectly. Always discuss any medications or supplements with your doctor before the test.
  1. 1
    MedlinePlus — Laboratory TestsSource
  2. 2
    Lab Tests OnlineSource
  3. 3
    Mayo Clinic — Tests & ProceduresSource

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.

Medical Disclaimer

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