---
title: "What does a low eGFR (Cystatin C) mean?"
type: biomarker-interpretation
url: "https://www.test-well.com/biomarkers/egfr-cystatin-c/low"
biomarker: eGFR (Cystatin C)
direction: low
reference_range:
  - "age 18+: 60.0 – 120 mL/min/1.73m2"
reviewed_at: 2026-09-08
review_status: reviewed
date_published: 2026-09-05
---

# What does a low eGFR (Cystatin C) mean?

> A low cystatin C–based eGFR means the kidneys are filtering below expected for age. Because cystatin C is not inflated by muscle mass, meat or creatine, it is a more trustworthy kidney signal than creatinine in athletes, older adults and people with low muscle mass — though thyroid disease, steroids and obesity can lower it without kidney change. Below 60 for three months defines chronic kidney disease.


## When does this result need same-day care?

- A sharp fall from a recent value, very little urine, or swelling with breathlessness — same-day care

## What is the normal range for eGFR (Cystatin C)?

- age 18+: 60.0 – 120 mL/min/1.73m2

Sustained values below 60 can indicate chronic kidney disease.

## What are the common causes of low eGFR (Cystatin C)?

1. Chronic kidney disease: diabetes, hypertension, glomerular disease, polycystic kidney disease
2. Acute kidney injury: dehydration, NSAIDs, contrast, infection
3. Hyperthyroidism, high-dose corticosteroids (raise cystatin C, lower this eGFR)
4. Obesity, smoking, inflammation (modest)
5. Normal aging (eGFR falls ~1 mL/min per year after 40)

## What symptoms go with low eGFR (Cystatin C)?

- Usually none until well below 30
- Fatigue, swelling, foamy urine, nocturia, itching as kidney disease progresses

## What do clinicians usually check next?

- Creatinine-based eGFR at the same draw; the combined equation is the most reliable single number
- Urine albumin-to-creatinine ratio
- Blood pressure, A1c, TSH, medication review (NSAIDs, PPIs, lithium)
- Repeat in 3 months to confirm before any CKD label; nephrology referral below 45 or if falling fast

Follow-up tests at TestWell: [TSH (Thyroid Stimulating Hormone)](https://www.test-well.com/tests/tsh) ($26.99), [TSH + Free T4](https://www.test-well.com/tests/tsh-with-free-t4) ($27.99).

## How do you recheck eGFR (Cystatin C)?

| Test or panel | Type | Price | Fasting | Results |
| --- | --- | --- | --- | --- |
| [Kidney Health Panel](https://www.test-well.com/tests/kidney-health-panel) | Panel (4 tests) | $64.99 | Yes | 2–4 business days |
| [Total Body Panel](https://www.test-well.com/tests/total-body-panel) | Panel (49 tests) | $499.99 | Yes | 5–10 business days |
| [Renal Panel](https://www.test-well.com/tests/renal-panel) | Test | $23.99 | No | 2–4 business days |

Plus one $6 lab processing fee per order; physician authorization included.

## Common questions

### My creatinine eGFR is normal but the cystatin C eGFR is low — which is right?

Possibly the cystatin C one: creatinine underestimates kidney disease in people with low muscle mass. The reverse mismatch happens in muscular people. When they disagree, clinicians use the combined equation and the urine albumin to decide.

## Related

- [eGFR (Cystatin C) reference ranges](https://www.test-well.com/biomarkers/egfr-cystatin-c)
- [Glucose reference range](https://www.test-well.com/biomarkers/glucose)
- [Creatinine reference range](https://www.test-well.com/biomarkers/creatinine)
- [eGFR reference range](https://www.test-well.com/biomarkers/egfr)

## Sources

- [National Kidney Foundation](https://www.kidney.org/atoz/content/gfr)
- [Testing.com (AACC) — Cystatin C Test: What It Measures and How It Works](https://www.testing.com/tests/cystatin-c/)

---

Medically reviewed by Youmna DiStefano, MD (Medical Reviewer, TestWell); last reviewed 2026-09-08. Review policy: https://www.test-well.com/editorial-policy

Canonical page: https://www.test-well.com/biomarkers/egfr-cystatin-c/low
Machine-readable catalog: https://www.test-well.com/api/catalog.json · MCP server: https://www.test-well.com/mcp · Overview for agents: https://www.test-well.com/llms.txt

Prices are cash-pay, in USD, and include physician authorization; every order adds one flat $6 lab processing fee. Educational content is not a diagnosis — discuss results with a clinician.