Creatinine and eGFR: Reading Your Kidney Report
eGFR — estimated glomerular filtration rate — is the number that tells you how well your kidneys are filtering, and it is calculated from your blood creatinine result along with your age and sex. Creatinine on its own is a waste product; the eGFR converts it into something interpretable. An eGFR of 90 or above is considered normal filtering, and chronic kidney disease is staged from G1 to G5 as that number falls. Stage alone does not decide treatment, because the amount of protein in your urine matters just as much.
What creatinine actually is
Creatinine is a waste product produced by normal muscle activity. Healthy kidneys filter it out into urine at a steady rate. When filtering slows, creatinine accumulates in the blood — so a rising creatinine level is an indirect signal that filtration has fallen.
Because it comes from muscle, creatinine is influenced by body build. A muscular young man and a slight older woman can have the same creatinine value and quite different kidney function. This is exactly why the raw number is converted into eGFR before it is interpreted.
What eGFR means
eGFR estimates how many millilitres of blood your kidneys clear per minute, adjusted to a standard body size. It is reported in mL/min/1.73m². Higher is better. The word 'estimated' is doing real work: it is a calculation, not a direct measurement, and it is least reliable at the extremes of body composition.
The five stages of chronic kidney disease
International KDIGO guidance defines stages by eGFR as follows. Note that stages G1 and G2 require evidence of kidney damage — usually protein in the urine — because a normal eGFR by itself is not a disease.
| Stage | eGFR | What it describes |
|---|---|---|
| G1 | 90 or above | Normal filtration, with other evidence of kidney damage |
| G2 | 60–89 | Mildly reduced filtration, with evidence of damage |
| G3a | 45–59 | Mild to moderate reduction |
| G3b | 30–44 | Moderate to severe reduction |
| G4 | 15–29 | Severely reduced filtration |
| G5 | Below 15 | Kidney failure; dialysis or transplant is usually discussed |
Reaching stage G5 does not mean dialysis starts that day. The decision to begin depends on symptoms, blood chemistry, and fluid balance — not on a single threshold being crossed.
Why urine protein matters as much as eGFR
Two people can share an eGFR of 50 and face very different outlooks. The one with significant albumin in the urine is at markedly higher risk of progression than the one without. Modern staging therefore pairs the eGFR grade with an albuminuria category (A1, A2, A3). If your report gives only an eGFR, ask whether a urine albumin-to-creatinine ratio has been done.
Why one reading is never the whole story
A single eGFR can be misleading for ordinary reasons. Dehydration, a heavy protein meal, intense exercise, and some medications all shift creatinine temporarily. Chronic kidney disease is defined by abnormality persisting beyond three months, which is why a repeat test is standard rather than a sign of doubt.
What matters most clinically is the trend. A stable eGFR of 45 held for years is a different situation from an eGFR that has fallen from 70 to 45 within a year. Keep your reports in date order and bring them to appointments — that sequence is often more informative than the newest value alone.
Questions worth asking at your next appointment
- What is my eGFR, and what was it at my previous test?
- Has my urine albumin been checked, and what was the result?
- At my current stage, how often should I be retested?
- Are any of my current medicines affecting my kidneys or their dosing?
- What blood pressure and blood sugar targets should I be aiming for?
Common questions
Is a creatinine of 1.5 dangerous?
It cannot be interpreted on its own. The same creatinine value corresponds to very different eGFR results depending on age, sex, and body build. Ask for the eGFR calculated from that creatinine, and for a urine albumin result alongside it.
Can eGFR improve?
It can rise modestly when a temporary cause is corrected — dehydration, an infection, or a medication effect. Established chronic kidney disease is generally not reversed, but its decline can often be slowed considerably with good blood pressure and blood sugar control.
Does a normal eGFR mean my kidneys are fine?
Not necessarily. Kidney damage can be present with a normal eGFR, which is why stages G1 and G2 exist. Protein in the urine can appear well before filtration falls, so both tests are needed.
Sources
- KDIGO Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease — Kidney Disease: Improving Global Outcomes (KDIGO)
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