eGFR and Creatinine: What They Are and How to Read Your Kidney Numbers

Creatinine is a waste product your kidneys filter out, and eGFR is an estimate of how fast they're filtering — calculated from your creatinine, age, and sex — so the two are really one story about kidney function. Creatinine is the raw measurement; eGFR (estimated glomerular filtration rate) translates it into a more interpretable "how well are the kidneys clearing waste" number. Creatinine is also one of the nine markers behind the Levine PhenoAge biological age score.¹

What are creatinine and eGFR, and why they matter

Creatinine is produced steadily as muscle breaks down, and healthy kidneys clear it at a fairly constant rate. So when kidney filtering slows, creatinine rises in the blood. The catch: creatinine also depends on muscle mass, so a muscular person and a frail one can filter identically yet show different creatinine values. eGFR corrects for some of this by folding in age and sex, giving a number scaled to a standard body size (mL/min/1.73m²). The current standard equation, the 2021 CKD-EPI creatinine formula, was updated to remove the race coefficient.² eGFR is why clinicians can compare kidney function across very different people — and why it's read alongside a urine albumin test, which catches kidney damage creatinine alone can miss.

What's a normal or optimal eGFR or creatinine level?

Two different questions, two answers:

• The creatinine lab reference range (what's typical) is commonly printed as roughly 0.7–1.3 mg/dL for men and 0.6–1.1 mg/dL for women, varying by lab and muscle mass — read your value against the range on your report.³
• eGFR and guideline thresholds. An eGFR of ≥60 mL/min/1.73m² is generally considered normal in the absence of other signs of kidney damage. The KDIGO clinical guidelines define chronic kidney disease as an eGFR below 60 — or other markers of kidney damage such as albuminuria — persisting for at least three months.⁴ A single low eGFR isn't a diagnosis; the definition deliberately requires time and repeat testing.

There isn't one "optimal" number here. eGFR naturally declines somewhat with age, the estimate is less accurate at unusual muscle mass, and a value only means something in the context of your urine albumin, your trend, and your history.

How to track your kidney function over time

A single eGFR is a dot, and because creatinine wobbles with hydration and diet, one reading can mislead. Kidney disease is defined by persistence, so the trend across several draws is exactly what matters most.

This is the job Libby is built for: drop in a lab PDF and every creatinine and eGFR result lands on one timeline, against the range on each report, so you can see a genuine trajectory instead of a lonely value. Read the trend, not the dot — see how to read your blood test results for why that habit matters.

Related markers

Read your kidney numbers in company:

• Albumin — blood albumin is a general-health protein, while a urine albumin test catches early kidney damage; both round out the picture, and albumin is a biological-age marker too.
• ALT and AST — liver enzymes often drawn on the same comprehensive metabolic panel, giving organ-function context.

FAQ

Is a low eGFR always kidney disease? No. eGFR is an estimate that dips with dehydration, high muscle mass, or a single off day, and it drifts down gradually with age. KDIGO requires a low value (or other damage markers) to persist for three months before it's called chronic kidney disease — which is why the trend, not one reading, is decisive.

Do I need to fast for a creatinine test? Creatinine is often part of a metabolic panel that may require fasting, and a very high-protein meal beforehand can nudge it. Follow your order's instructions and keep conditions consistent so your trend stays comparable.

Why is creatinine used to estimate biological age? The Levine PhenoAge algorithm uses creatinine as one of nine routine markers whose combination tracks with population health outcomes. It's a model input, not a standalone verdict — see our biological age test guide.

Educational content, not medical advice. This article is for general information and personal record-keeping. Reference ranges vary by lab and by person, and any figures here are attributed to the sources named, not Libby recommendations. Always talk to a qualified healthcare professional about your results.