Quick Facts
- Sample: Venous blood (serum)
- Fasting: Not required
- Turn-around: 3–5 business days. May take longer due to weather, holidays, or lab delays.
Benefits
- More accurate than creatinine alone — unaffected by muscle mass, diet, sex, or race for better early detection
- Detects kidney decline sooner — identifies reduced function before creatinine becomes abnormal
- Supports cardiovascular risk assessment — elevated levels predict heart disease and mortality risk
- Convenient self-monitoring — order without a specialist visit and track trends over time
- Fast results — secure online delivery in 1–2 days to help guide next steps
Who Is This Test For?
- Adults with diabetes, hypertension, or cardiovascular disease at higher CKD risk
- Individuals with very high or very low muscle mass where creatinine may be misleading
- Older adults, frail patients, or those with muscle-wasting conditions
- People taking potentially nephrotoxic medications needing kidney monitoring
- Anyone with normal creatinine but risk factors suggesting early kidney disease
- Those seeking proactive kidney health tracking without facility fees
How It Works – Just 3 Steps
- Order online — No physician referral required; select your test and receive lab requisition instantly
- Visit a local lab — A phlebotomist collects a blood sample at your convenience
- Review results securely — Access your results online and share with your provider
FAQ
What does cystatin C measure? Cystatin C is a protein produced constantly by your cells and filtered by the kidneys; higher levels indicate reduced kidney function.
How is this different from a creatinine test? Unlike creatinine, cystatin C isn't influenced by muscle mass, diet, age, sex, or race, making it more reliable for early kidney disease detection (Testing.com 2021; Mayo Clinic 2023).
Do I need to fast before this test? No fasting is required, and you can continue routine medications unless advised otherwise by your provider.
Can I order this test without a doctor's visit? Yes, Walk-In Lab offers direct-access testing in most states, allowing you to self-screen and monitor kidney health affordably.
What if my results are abnormal? Elevated cystatin C suggests reduced kidney function; discuss results with your provider for eGFR calculation, repeat testing, or further evaluation.
Should I use this instead of creatinine? Cystatin C complements rather than replaces creatinine; combined equations improve accuracy and risk prediction for CKD progression and cardiovascular events (CKD-EPI 2021).
More Details
What is the purpose of this test?
The Cystatin C Blood Test evaluates kidney function by measuring a protein produced at a constant rate by all nucleated cells and cleared almost entirely through glomerular filtration. Higher cystatin C levels reflect reduced kidney filtering capacity (lower GFR). Unlike creatinine-based tests, cystatin C is minimally affected by muscle mass, diet, sex, or race, making it particularly valuable for detecting early or subtle kidney impairment where creatinine appears normal. This test provides a refined view of kidney health, supporting proactive monitoring in people with diabetes, hypertension, cardiovascular risk, or those on nephrotoxic medications (Testing.com 2021; Mayo Clinic 2023).
Who would benefit from this test?
This test is especially useful for people where creatinine-based estimates may be misleading. You would benefit if you have risk factors for chronic kidney disease (CKD) such as diabetes, hypertension, cardiovascular disease, or older age. It's particularly valuable for very muscular individuals, older adults with muscle wasting, obese patients, or those with malnutrition, since cystatin C isn't influenced by body composition. People taking medications that can harm the kidneys, those with a family history of kidney disease, and individuals needing cardiovascular risk stratification also benefit from this more accurate marker (NKF-ASN Task Force 2021; Cleveland Clinic 2025).
When should I order Cystatin C w/o eGFR?
Consider ordering this test when creatinine-based eGFR seems inconsistent with your clinical risk profile, or when you have concern for early CKD despite "normal" creatinine results. It's useful if you have conditions affecting muscle mass—such as frailty, extreme obesity, malnutrition, or chronic illness—that may bias creatinine results. Order if you're monitoring kidney function over time in response to therapy or lifestyle changes, or if you need baseline kidney assessment before starting potentially nephrotoxic treatments. This test is also valuable for cardiovascular risk stratification, as elevated cystatin C predicts heart disease and mortality risk (KDIGO/CKD-EPI 2021; MedlinePlus 2022).
How do I interpret the results?
Laboratories report cystatin C in mg/L with an adult reference range (exact values vary by lab). Results above the upper limit generally indicate reduced kidney function and possible CKD, while values within the normal range suggest preserved filtration. However, interpretation should consider your age, comorbidities, and medications. For deeper insight, your clinician can use your cystatin C value—alone or combined with creatinine, age, and sex—in CKD-EPI equations to calculate eGFR and stage CKD if present. Combined creatinine-cystatin C equations provide the most accurate risk prediction for kidney disease progression, cardiovascular events, and mortality (Testing.com 2021; Mayo Clinic 2023).
Within reference range (typically 0.53–0.95 mg/L):
- What it means: Normal kidney function with adequate glomerular filtration
- Typical action: Continue routine monitoring if risk factors are present; maintain a kidney-healthy lifestyle
Mildly elevated (0.96–1.50 mg/L):
- What it means: Possible mild to moderate reduction in kidney function
- Typical action: Calculate eGFR, repeat testing, evaluate for secondary causes, and optimize blood pressure and glucose control
Moderately elevated (1.51–2.50 mg/L):
- What it means: Moderate to severe reduction in kidney function; chronic kidney disease (CKD) likely
- Typical action: Refer to nephrology, check urine albumin, adjust medications, and implement a CKD management plan
Severely elevated (>2.50 mg/L):
- What it means: Severe kidney impairment; advanced CKD or possible kidney failure
- Typical action: Urgent nephrology consultation, comprehensive CKD staging, and evaluation for dialysis or transplant planning
CKD affects approximately 14–15% of U.S. adults, but early stages are frequently under-diagnosed because creatinine may remain normal until roughly half of kidney function is lost (NKF 2022).
Disclaimer: Reference ranges may vary by laboratory. Listed ranges are general guidelines and may differ from those used by the performing lab. Always consult your healthcare provider for interpretation.
Pre-test preparation
No fasting is required for a cystatin C test, and you should continue routine medications unless your clinician advises otherwise. For the most accurate baseline assessment, schedule your test when you're clinically stable—acute illness, recent imaging contrast, or dehydration can transiently affect kidney function. Avoid scheduling immediately after strenuous exercise or during active infections. Stay well-hydrated before your blood draw. If you're taking medications known to affect kidney function (such as NSAIDs), inform your provider, though you typically won't need to discontinue them for testing.
How often should I get tested?
- Healthy adults with no risk factors: Every 3–5 years as part of routine wellness screening
- Adults with diabetes, hypertension, or cardiovascular disease: Annually, or as recommended by your provider
- Established CKD (stages 1–2): Every 6–12 months to monitor progression
- Established CKD (stages 3–4): Every 3–6 months, or more frequently per nephrology guidance
- Taking nephrotoxic medications: Baseline testing, then every 3–6 months during treatment
- Abnormal or borderline results: Repeat in 3 months to confirm trends and guide management
Why early detection matters
Early detection of kidney disease through cystatin C testing allows for timely interventions that can slow or prevent progression to kidney failure. CKD is often asymptomatic in early stages, and creatinine may remain normal until approximately 50% of kidney function is lost. Cystatin C detects subtle reductions earlier, giving you and your provider a critical window to implement protective measures. Elevated cystatin C is also a strong independent predictor of cardiovascular events and mortality—in large U.S. population studies, it predicts 20-year cardiovascular and all-cause death risk even after adjusting for traditional factors (NIH CKD-Prognosis Consortium 2025). Early intervention through blood pressure control, glucose management in diabetes, medication adjustments, and lifestyle modifications can preserve kidney function, reduce cardiovascular risk, and significantly improve long-term health outcomes.
Related tests you may consider
Serum Creatinine with eGFR — Pairs well with cystatin C because combined creatinine-cystatin C equations provide more accurate GFR estimates and better prediction of CKD progression and cardiovascular events than creatinine alone (Frontiers in Medicine 2024).
Urine Albumin-to-Creatinine Ratio (uACR) — Detects albumin leakage into urine, an early sign of kidney damage; together with cystatin C, uACR helps stage CKD and refine cardiovascular and renal risk stratification (MedlinePlus 2022).
Comprehensive Metabolic Panel (CMP) — Offers broader metabolic insight including electrolytes, bicarbonate, glucose, and liver markers; combined with cystatin C, it helps distinguish kidney-specific issues from other systemic conditions affecting overall health (Testing.com 2021).
