Kidney Function Test Explained: Creatinine, eGFR and Urea
What creatinine, eGFR, urea, BUN, uric acid and electrolytes on a kidney function test mean, with typical ranges, CKD stages and when to see a doctor.
By Browser Tools Team · · 3 min read
A kidney function test shows how well your kidneys filter waste from your blood. The key number is eGFR: 90 or more is normal, 60–89 is mildly decreased, and below 60 for three months or more suggests chronic kidney disease. eGFR is calculated from creatinine, a muscle waste product, together with your age and sex.
The free Kidney Function Test Checker explains each result and calculates eGFR from your creatinine with the race-free CKD-EPI 2021 equation. It runs in your browser, so your results stay private.
What does each kidney test measure?
| Test | What it shows | Typical adult range |
|---|---|---|
| Creatinine | Muscle waste filtered by the kidneys | Men 0.74–1.35 mg/dL (65–119 µmol/L), women 0.59–1.04 mg/dL (52–92 µmol/L) |
| eGFR | Estimated filtering rate | 90+ mL/min/1.73m² |
| Blood urea | Protein waste product | 15–45 mg/dL (about 2.5–7.5 mmol/L) |
| BUN (urea nitrogen) | The nitrogen part of urea | 7–20 mg/dL |
| Uric acid | Purine waste, linked to gout | Men 3.4–7.0 mg/dL, women 2.4–6.0 mg/dL |
| Sodium | Salt and water balance | 135–145 mmol/L |
| Potassium | Nerve and heart function | 3.5–5.1 mmol/L |
Some labs report urea and others BUN. Ranges vary between labs, so compare with your report. To convert creatinine from mg/dL to µmol/L, multiply by 88.4.
What are the stages of kidney function?
| eGFR | Stage | Meaning |
|---|---|---|
| 90 or more | G1 | Normal |
| 60–89 | G2 | Mildly decreased |
| 45–59 | G3a | Mildly to moderately decreased |
| 30–44 | G3b | Moderately to severely decreased |
| 15–29 | G4 | Severely decreased |
| Below 15 | G5 | Kidney failure range |
Stages G1 and G2 count as chronic kidney disease only if there's other evidence of kidney damage, such as protein in the urine. eGFR naturally falls a little with age. A single low result isn't a diagnosis; doctors look for a result that stays low for three months or more.
What makes creatinine and urea go up?
Short-term rises are common with dehydration, vomiting or diarrhoea, a large meat meal before the test, intense exercise, and some medicines (including some painkillers like ibuprofen and some blood pressure tablets). Longer-term rises can come from diabetes, high blood pressure, kidney infections or blockages.
Because creatinine depends on muscle, very muscular people can have a higher creatinine with healthy kidneys, and people with low muscle mass can look better than they are. Doctors may add a cystatin C test or a urine albumin test (ACR) for a clearer picture.
Potassium matters a lot in kidney disease. Too high or too low affects the heart rhythm, which is why very abnormal potassium is treated as urgent.
How do I check my kidney results?
- Open the Kidney Function Test Checker. It opens on the kidney group.
- Paste the report text, upload a digital PDF, or choose Enter values and type creatinine, urea or BUN, uric acid and electrolytes.
- Enter your sex and age. The checker then adds an eGFR line, calculated from creatinine, age and sex (CKD-EPI 2021), if your report doesn't already show one.
- Read the stage, explanation and questions for your doctor.
How can I protect my kidneys?
Control blood pressure and blood sugar, which are the two biggest causes of kidney disease. Limit salt, stay active, don't smoke, and avoid regular use of anti-inflammatory painkillers without medical advice. Drink enough water unless your doctor has told you to limit fluids.
Diet for kidney disease is very individual: protein, potassium and phosphorus limits depend on your stage and blood tests, and dialysis diets are completely different. Our Kidney Disease Diet Plan explains the principles, but please follow your renal dietitian. The High Blood Pressure Diet Plan helps with salt.
When should I see a doctor urgently?
Seek same-day care for very high potassium (the checker warns above about 6.2 mmol/L), very low sodium, a sudden large rise in creatinine, passing very little urine, swelling with breathlessness, or confusion.
Read how to read a blood test report, or check your kidney results now.
Frequently asked questions
What is a normal eGFR?
An eGFR of 90 or above is normal. 60–89 is mildly decreased and is often normal for older adults if there's no other sign of kidney damage. Below 60 for three months or more is a sign of chronic kidney disease.
What is a normal creatinine level?
Typical adult ranges are about 0.74–1.35 mg/dL (65–119 µmol/L) for men and 0.59–1.04 mg/dL (52–92 µmol/L) for women. Muscle mass affects creatinine, so eGFR is usually the better guide.
Can dehydration raise creatinine?
Yes. Dehydration, a big meat meal, hard exercise and some medicines can raise creatinine and urea temporarily. That's why an abnormal result is usually repeated.
How is eGFR calculated?
eGFR is estimated from your creatinine level, age and sex. Many labs now use the CKD-EPI 2021 equation, which doesn't use race. The checker calculates it the same way when you give your age and sex.
Sources
- #kidney
- #egfr
- #creatinine
- #lab results