Cystatin C levels, explained
Cystatin C is a small protein made by every cell at a steady rate and cleared only by the kidneys — a measure of kidney filtration that, unlike creatinine, is not skewed by muscle mass.
What’s a normal Cystatin C level?
Typical adult reference range, shown for orientation. Your report’s range may differ by lab, age, and sex — the analyzer uses your report’s own ranges when available.
What high and low Cystatin C mean
A value outside the reference range is a flag, not a diagnosis. Here’s what each direction usually points to — and the most common causes.
High cystatin C means the kidneys are clearing it more slowly — reduced filtration (lower eGFR) — though thyroid disease, steroids and obesity can raise it without kidney damage.
- Chronic kidney disease from diabetes, hypertension, or glomerular disease
- Acute kidney injury (dehydration, medications, contrast dye, infection)
- An overactive thyroid, corticosteroid treatment, obesity, or smoking (non-kidney causes)
- Inflammation or cancer, which modestly increase production
A low cystatin C is not usually a concern — it reflects good filtration, and is also seen with an underactive thyroid.
- Normal or above-average kidney filtration
- Hypothyroidism (lowers production)
When a Cystatin C result needs attention
A cystatin C-based eGFR below 60 mL/min/1.73 m² persisting for three months indicates chronic kidney disease and should be reviewed; a sudden rise, or a level over ~1.5 mg/L with reduced urine output, swelling or breathlessness, needs prompt evaluation.
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Cystatin C — frequently asked questions
- What does high cystatin C mean?
- Most often that kidney filtration is reduced — the kidneys are clearing cystatin C more slowly, which lowers the estimated GFR. It can also be modestly raised by an overactive thyroid, steroid medication, obesity, smoking or inflammation without any kidney damage, which is why a high value is interpreted alongside creatinine, UACR and your history.
- Cystatin C vs creatinine — which is more accurate?
- Neither is perfect, but cystatin C is less affected by muscle mass, diet and sex, so it is more reliable in people who are very muscular, elderly, frail, pregnant, amputees, or eating little protein. Guidelines recommend using the two together: an eGFR calculated from both is the most accurate routine estimate available.
- What is a normal cystatin C level?
- Roughly 0.6–1.0 mg/L in adults, rising slightly with age; ranges differ between assays, so compare with the reference range printed on your report. Values above about 1.0 mg/L generally correspond to an eGFR below 90, and above about 1.3–1.5 mg/L to an eGFR below 60.
Related lab markers
- Creatinine →Creatinine is a muscle waste product cleared by the kidneys — the standard blood marker used to estimate kidney function.
- UACR (Urine Albumin-to-Creatinine Ratio) →UACR measures how much albumin (a blood protein) is leaking into your urine, corrected for urine concentration — it is the earliest routine sign of kidney damage.
- TSH (Thyroid-Stimulating Hormone) →TSH is the pituitary hormone that tells your thyroid how hard to work — it is the primary screening test for thyroid function.
- All lab markers →Browse every biomarker guide in one place.
This page provides educational health information and does not replace professional medical advice, diagnosis, or treatment. Interpret any lab value with your clinician, who has your full medical context. For emergencies, contact emergency services.