Cystatin C
A more accurate kidney marker than creatinine — especially if you're muscular, take creatine, or want to catch kidney decline early.
Cystatin C measures kidney filtration without being influenced by your muscle mass or diet. It catches kidney decline years before creatinine does — and it's also an independent predictor of cardiovascular risk and longevity.
What is this test?
Cystatin C is a small protein produced at a constant rate by every cell in your body that has a nucleus. Your kidneys filter it out of your blood, and — unlike creatinine — its production doesn't change based on how muscular you are, what you eat, or whether you take creatine.
That makes it a much more reliable gauge of how well your kidneys are actually filtering. If your creatinine looks borderline but you lift weights or supplement creatine, cystatin C gives you the real answer.
What your number means
| Cystatin C | What it suggests |
|---|---|
| < 0.55 mg/L | Very low — uncommon, usually not clinically significant |
| 0.55–0.85 mg/L | Optimal — healthy kidney filtration |
| 0.85–1.0 mg/L | Upper-normal — worth monitoring annually |
| > 1.0 mg/L | Elevated — may indicate early kidney function decline or cardiovascular risk |
The combined creatinine + cystatin C eGFR equation (CKD-EPI 2021) is the most accurate non-invasive kidney function estimate available. If you're adding cystatin C, ask your doctor to calculate this combined eGFR.
How to keep your cystatin C low
Cystatin C reflects your kidney filtration rate, so improving it means protecting your kidneys:
- Control blood pressure — hypertension is the #1 driver of kidney decline. Target < 130/80 mmHg
- Manage blood sugar — diabetes and insulin resistance damage kidney filtration over time
- Stay hydrated — chronic mild dehydration stresses your kidneys, especially in Indian summers
- Limit NSAIDs — regular ibuprofen or diclofenac use directly damages kidney tissue
- Reduce inflammation — cystatin C rises with systemic inflammation. Omega-3, curcumin, and exercise help
- Maintain healthy weight — obesity increases kidney workload and raises cystatin C independently
Track your kidney function over time
eterni connects cystatin C, creatinine, and eGFR into one trajectory — so you see trends before they become problems.
Get early accessFrequently Asked Questions
Why is cystatin C better than creatinine?
Creatinine is produced by your muscles, so it is affected by muscle mass, creatine supplements, high-protein diets, and exercise. Cystatin C is produced at a constant rate by all nucleated cells and is not influenced by any of these factors. This makes it far more accurate for people who are muscular, elderly, or on creatine.
Can cystatin C predict heart disease?
Yes. Multiple large studies show that elevated cystatin C independently predicts cardiovascular events, heart failure, and all-cause mortality — even after adjusting for kidney function. It appears to reflect vascular inflammation and endothelial dysfunction beyond just filtration.
Who should add cystatin C to their panel?
Anyone who is muscular, takes creatine, follows a high-protein diet, is elderly with low muscle mass, has borderline eGFR (60–89), or wants the most accurate kidney and longevity assessment. It is especially useful for the fitness-oriented population in India who supplement creatine.
Is cystatin C available in India?
Yes, but it is not part of standard panels. You will need to specifically request it. Major labs like SRL, Metropolis, and Thyrocare offer cystatin C testing, typically costing ₹1,200–2,500. It is worth adding annually if you fall into any of the groups who benefit from it.
Cystatin C as a longevity marker
Beyond kidney function, cystatin C has emerged as one of the strongest blood-based predictors of healthspan. Large cohort studies (Cardiovascular Health Study, NHANES) consistently show that higher cystatin C levels predict:
- All-cause mortality — even within the "normal" reference range, higher values predict shorter lifespan
- Heart failure risk — cystatin C outperforms creatinine-based eGFR for predicting cardiovascular events
- Cognitive decline — elevated levels are associated with faster age-related cognitive deterioration
- Frailty — cystatin C predicts physical function decline in older adults
When creatinine misleads
Creatinine gives you a falsely reassuring picture in several common scenarios:
- Elderly with low muscle mass — creatinine stays "normal" even as kidney function declines because less creatinine is being produced. A "normal" creatinine of 1.0 in a frail 75-year-old may mask significant kidney impairment.
- Muscular individuals and creatine users — the opposite problem. Higher muscle mass or creatine supplementation raises creatinine, flagging "kidney disease" when kidneys are perfectly healthy.
- High-protein dieters — large protein meals (especially red meat) transiently raise creatinine.
In all of these cases, cystatin C gives you the accurate answer.
Know what's working. Know what's not.
eterni connects your lab results, supplements, and retests — so you can see the trajectory, not just a snapshot.
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