Creatinine
Serum Creatinine
What this test measures
Creatinine is a waste product made by your muscles. Healthy kidneys remove it from your blood. This test measures how much creatinine is in your blood. High levels can mean your kidneys are not working properly.
Understanding the numbers
Typical range: Men: 59-104 µmol/L | Women: 45-84 µmol/L
Normal ranges can vary slightly. Muscular people may naturally have higher levels.
- Low — usually low muscle mass: 30–45 µmol/L
- Normal (women): 45–84 µmol/L
- Overlap: 84–104 µmol/L
- Raised: 104–200 µmol/L
- Markedly raised: 200–400 µmol/L
Key numbers
- 84 µmol/L — Women — upper limit of normal
- 104 µmol/L — Men — upper limit of normal
- 150 µmol/L — Significant — needs GP review
- 200 µmol/L — Marked rise — urgent review; consider AKI
Normal ranges are typical UK lab values and vary slightly between labs. Creatinine on its own is less useful than eGFR, which adjusts for age and sex. A rise in creatinine of more than 26 µmol/L in 48 hours, or 1.5× baseline within 7 days, meets the AKI definition (NICE NG148).
Ranges can vary slightly between laboratories — your report may show slightly different numbers. This page does not read or interpret your result; your GP looks at it alongside your history and other tests.
What a higher-than-normal result can mean
- Your kidneys may not be filtering waste properly
- This could be a sign of kidney problems
- Dehydration can temporarily raise creatinine
- Some medicines can also affect levels
When not to wait
A sudden rise in creatinine is acute kidney injury. Don't wait if you feel unwell and know your kidney function has changed.
- Passing very little or no urine over a day
- Vomiting or diarrhoea you cannot keep on top of
- Breathlessness or swollen ankles getting worse quickly
- Confusion, drowsiness, or feeling very unwell
- Known CKD with a new severe illness
- A new severe medicine reaction with reduced urine output
Call NHS 111 for urgent advice, or 999 if someone is seriously unwell.
Questions you could ask your GP
- Could any of my medicines be affecting my creatinine level?
- Do I need to have my eGFR calculated to check my kidney function?
- Should I drink more water or make any dietary changes?
- How often should this test be repeated?
Example stories
These are made-up examples to show how results are talked about in real appointments. They are not real patients.
Bodybuilder, 'high' creatinine
Ben's creatinine was 118 µmol/L. His eGFR was 72. He is 6'2", trains four times a week, and eats a lot of protein. Urine protein was negative.
What the GP said: “In someone with your muscle mass, creatinine runs a bit high and the eGFR formula slightly underestimates kidney function. This is almost certainly normal for you. We don't need to investigate — we'll just recheck next year.”
Creatinine comes from muscle. People with more muscle — weightlifters, manual workers, some men — have higher creatinine and apparently lower eGFR without actually having kidney disease. Context matters.
Frail and losing weight
Margaret's creatinine was 52 µmol/L and her eGFR was 78. She weighed 48 kg and her grip was weak.
What the GP said: “Your creatinine looks normal — but because you have very little muscle, your kidneys may actually be working less well than the eGFR suggests. We'll keep an eye on a urine protein test and be careful with medicine doses.”
What happened next: Margaret was flagged for careful dosing of any new medicines and her urine ACR was checked yearly.
Low or low-normal creatinine in a frail older adult can hide worse kidney function than the number suggests. Your GP interprets creatinine alongside weight, muscle, and age.
Admitted with sepsis
Thomas was admitted with a severe chest infection. His baseline creatinine last year was 92 µmol/L; today it was 248. That is an acute kidney injury.
What the GP said: “Your kidneys have been hit hard by the infection and dehydration. We're giving fluids, treating the infection, and pausing your ACE inhibitor and diuretic. We expect the creatinine to come down over a few days.”
What happened next: Over five days in hospital Thomas's creatinine fell back to 110 µmol/L. At six weeks it was back to his baseline of 94 and his ACE inhibitor was restarted.
Acute kidney injury during a severe illness is common and often reversible. Pausing medicines that stress the kidneys (ACE inhibitors, diuretics, NSAIDs) is a standard part of the treatment — not a permanent change.
Stable long-standing rise
Rohit has had hypertension and Type 2 diabetes for 20 years. His creatinine has been sitting around 150-160 for two years. His eGFR is 42.
What the GP said: “Your creatinine is stably raised because of long-standing diabetes and blood pressure affecting the kidneys — this is CKD stage 3b. We'll keep your blood pressure tight, avoid ibuprofen, and review your medicines yearly.”
What happened next: Rohit was started on dapagliflozin, and his creatinine and urine protein both improved over six months.
A stable raised creatinine in someone with long-standing diabetes or blood pressure usually means established CKD. The goal is to slow further decline rather than to 'fix' the number. Small, steady rises over years are expected; sudden rises are not.
Before you act on anything here
This page is general information, written to help you understand — it is not personal medical advice and it cannot tell you what is right for you. Talk to your own GP, pharmacist or nurse about your own health.
- Need help now but it's not an emergency? Call NHS 111 or use 111.nhs.uk.
- Emergency? Call 999 or go to A&E.