Cystatin C

Blood

Kidney Function

Cystatin C is a protein produced by nearly all cells at a steady rate and cleared by the kidneys, making it an alternative and often more precise marker of kidney filtration. Unlike creatinine, it is not affected by muscle mass, so a preventive practice values it for assessing kidney function in muscular or older individuals.

What It Measures

Alternative GFR marker; not affected by muscle mass (unlike creatinine); more accurate kidney function in elderly and muscular individuals

Optimal vs. Lab Range

Longevity Optimal

0.6–0.85 mg/L

Target range for optimal health and longevity based on research.

Standard Lab

0.6–1.0 mg/L

Population-based reference range from standard labs.

Why It Matters

Cystatin C offers a refined view of kidney health, and it can reveal problems that creatinine-based estimates miss, particularly in people whose muscle mass distorts creatinine readings. A high level reflects reduced kidney filtration and is also associated with cardiovascular risk and inflammation, and notably it independently predicts mortality even when creatinine appears normal. A low level is generally not significant. Because it provides a clearer picture of true filtration in the elderly and in very muscular individuals, cystatin C strengthens long-term risk assessment when read alongside creatinine, eGFR, and urinary albumin.

When Low

Generally not significant when low

When High

Kidney dysfunction, cardiovascular risk, inflammation; independently predicts mortality even when creatinine normal

How to Optimize

As a kidney marker, cystatin C is improved indirectly by protecting kidney function rather than targeted on its own. Physician-directed kidney-protective strategies and blood pressure management are central, along with broader cardiovascular and metabolic health that reduces stress on the kidneys. Because an elevated cystatin C can flag risk before creatinine changes, it is a useful prompt for closer monitoring and preventive action. It is best interpreted together with creatinine, eGFR, and BUN. Targets and treatment are individualized with your physician; this content is educational and not a substitute for medical advice.

Key Interventions & Linked Compounds

Moderate evidence

Key Interventions

Kidney-protective protocols

BP management

Linked Compounds & Supplements

NAC

Omega-3

CoQ10

Curated from clinical literature. Individual results vary; consult a qualified clinician before changing a protocol.

Ordering Notes

Specimen

Serum or plasma (venous draw)

Patient prep

No fasting required. Maintain usual diet and medications unless advised.

Recommended cadence

Annual

Reporting unit

Confirm with the performing lab — units vary by region.

Pre-analytic notes

Standardize draw time of day, hydration, and recent exercise. Note any acute illness, supplements, or hormonal therapies on the requisition.

Recommended Follow-Up Actions

1
Confirm the result is reliable
Repeat abnormal values before acting — preferably from the same lab, same time of day, and under consistent prep. Rule out acute illness, recent intense exercise, or medication effects that can shift Cystatin C.
2
Compare against optimal, not just lab range
Use the optimal window above as the target. Lab "normal" is built from the general population and often misses early dysfunction.
3
Pair with related markers
Order a complementary panel covering metabolic, inflammatory, and hormonal context to interpret this marker properly.
4
Discuss interventions with a clinician
Use the interpretation guidance above to frame the conversation. Bring trends, not just one datapoint, to your visit.
5
Re-test on a defined cadence
If a change is implemented, re-measure in 8–12 weeks for fast-moving markers, or 3–6 months for slower ones, to confirm response before escalating.