It's one of the sentences I hear most in clinic: "I've been told my creatinine is high and I don't know what it means." Behind that number lies an important question —how your kidneys are working— but also a lot of nuance. A raised creatinine doesn't always mean serious kidney disease, and understanding it well is the first step to neither panicking nor dismissing it.
What creatinine and the filtration rate are
Creatinine is a substance the muscles produce steadily and the kidney clears through the urine. That's why its level in the blood is a good mirror of kidney function: if the kidney filters well, creatinine stays low; if it filters less well, it builds up and rises.
From creatinine, age and sex we calculate the estimated glomerular filtration rate (eGFR), which expresses roughly, as a percentage, how much the kidney is filtering. It is more useful than creatinine alone, and the value we usually use to classify kidney function.
Not every high creatinine is kidney disease
Before worrying, it helps to know that creatinine can rise from passing, reversible causes:
- Dehydration or a test done at a bad moment.
- Medicines that raise creatinine temporarily (some anti-inflammatories, certain antibiotics or other drugs).
- High muscle mass or a high intake of protein or supplements, which can give slightly higher figures without the kidney being diseased.
So, faced with an isolated high creatinine, the first step is often to repeat the test under good conditions and consider the context, rather than drawing conclusions from a single value.
A number is not a diagnosis. Creatinine is interpreted alongside your history, its trend over time and the rest of the blood test.
When it should be investigated
There are situations where a raised creatinine warrants assessment by Nephrology:
- When it stays high across several tests or rises gradually.
- If it comes with protein or blood in the urine.
- In people with hypertension, diabetes or a family history of kidney disease.
- If it appears suddenly (possible acute kidney injury), which needs prompt attention.
What we do in the clinic
The aim is to answer three questions: is this rise real and sustained? is it acute or chronic? and what is the cause? To do this we review your history and medication, repeat and extend the blood test (including a urine study), and in many cases perform a kidney ultrasound. With all of that we reach a diagnosis and a plan to protect kidney function and slow its decline.
The good news is that, when the cause is identified early, it can often be corrected or stabilised. Controlling blood pressure and glucose, adjusting medicines, staying well hydrated and proper follow-up make a real difference to the outlook.