Creatinine — the kidney marker behind your eGFR
Paired condition: Type 2 diabetes labs
Quick answer
Creatinine is a muscle-breakdown waste product your kidneys clear, so blood levels rise when kidney filtration falls. Its real value comes from converting it to eGFR (estimated glomerular filtration rate) using age and sex. The catch: creatinine depends heavily on muscle mass — a muscular person can look "worse" and a frail person "better" than their true kidney function, which is why creatinine is read as a trend and confirmed with additional markers, not judged on one value.
Reference ranges and interpretation
| Value / population | Classification | What it means |
|---|---|---|
| 0.7 – 1.3 mg/dL (men) | Typical | Standard adult male reference range; varies with muscle mass. |
| 0.6 – 1.1 mg/dL (women) | Typical | Standard adult female reference range. |
| eGFR ≥ 90 | Normal filtration | Stage G1 if no other kidney damage markers. |
| eGFR 60 – 89 | Mildly reduced | Stage G2; usually normal aging unless other signs. |
| eGFR < 60 for ≥ 3 months | CKD range | Stage G3+; warrants evaluation and monitoring. |
Creatinine alone is hard to interpret — always read the eGFR the lab calculates from it. A single high value can reflect dehydration, a hard workout, or high protein intake rather than kidney disease.
Why eGFR matters more than the raw number
What distorts creatinine
- Recent intense exercise — transiently raises it
- High protein / creatine supplements — can nudge it up
- Dehydration — concentrates it
- Some medications (e.g., trimethoprim, cimetidine) — raise creatinine without changing true filtration
What to check alongside creatinine
- Cystatin C — muscle-independent confirmation when creatinine is ambiguous
- Urine albumin-to-creatinine ratio (uACR) — detects kidney damage even when eGFR is normal
- BUN — nitrogen waste; the BUN/creatinine ratio helps distinguish dehydration from kidney causes
- HbA1c and blood pressure — diabetes and hypertension are the leading causes of CKD
Phi Longevity reads every marker on every lab you upload — together, against your history, against optimal ranges, and across time. The integrated picture tells you what a single number can't.
Start with my labs →Frequently asked questions
Should I be worried about one high creatinine?
Usually not on its own. Dehydration, a hard workout, a high-protein meal, or creatine supplements can raise it transiently. Kidney disease is defined by a reduced eGFR that persists for at least three months, so a single value is repeated and read as a trend before it means much.
Why did my eGFR change when the lab updated its equation?
In 2021 the standard CKD-EPI creatinine equation was refit to remove the race coefficient. Labs adopting it report slightly different eGFR values for the same creatinine. It's an equation change, not a change in your kidneys.
I lift weights — is my creatinine falsely high?
It can be. Greater muscle mass produces more creatinine at the same true filtration rate, so muscular people may show a mildly elevated creatinine and lower eGFR that overstates any kidney issue. Cystatin C, which doesn't depend on muscle, is the way to check.
What's the difference between creatinine and eGFR?
Creatinine is the measured blood value; eGFR is the estimated filtration rate calculated from it using age and sex. eGFR is what's used to stage kidney function because it standardizes creatinine across different body sizes.
References
All citations verified against PubMed / publisher of record (see note below for this page's verification date).
- 1.Inker LA, Eneanya ND, Coresh J, et al. (2021). New creatinine- and cystatin C-based equations to estimate GFR without race. New England Journal of Medicine. 385(19):1737-1749. — The 2021 race-free CKD-EPI equations, including the most-accurate creatinine + cystatin C version.PubMed →DOI →
- 2.Kidney Disease: Improving Global Outcomes (KDIGO) CKD Work Group. (2024). KDIGO 2024 Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease. Kidney International. 105(4S):S117-S314. — Definition and staging of CKD (eGFR < 60 for ≥ 3 months and/or damage markers); role of uACR.PubMed →DOI →
- 3.Levey AS, Stevens LA, Schmid CH, et al. (2009). A new equation to estimate glomerular filtration rate. Annals of Internal Medicine. 150(9):604-612. — The original CKD-EPI creatinine equation that eGFR reporting is built on.PubMed →DOI →
Reference ranges vary by lab, assay, and the eGFR equation in use. This page is educational and not a substitute for individualized medical advice.
By Steve Pinedo
Co-founder, Phi Longevity
Last updated: 2026-07-20
Steve Pinedo is the Co-founder of Phi Longevity, the AI application that turns a confusing stack of lab reports, wearable data, and clinical notes into a single, integrated picture of your health. He started Phi Longevity to make proactive health and wellness far easier to achieve. He realized how difficult it was for clients to manage their own care, records and coordination so he assembled a comprehensive M.D. led clinical team behind the platform, packaging the proactive-care experience that delivered measurable outcomes (lower triglycerides, reduced body fat, improved LDL, balanced hormones, relief from long-running autoimmune conditions) for any patient with a complicated lab to use now with an application. More about Phi Longevity →