Creatinine
Creatinine is a waste product your muscles make that your kidneys filter out — so it is one of the main ways to check how well your kidneys are working. A result inside your report's range usually means they are clearing waste as expected. A higher level can mean they are filtering less efficiently, though muscle, a hard workout or dehydration can nudge it too.
Standard CareWhat is creatinine?
Creatinine is a waste product that forms as your muscles use energy — it comes from the normal day-to-day breakdown of muscle tissue, and a little from the protein in your food. Your kidneys filter it out of your blood and pass it into your urine. Because your muscles produce it at a fairly steady rate, the level left in your blood is a useful mirror of how well your kidneys are clearing waste. One thing to know: the more muscle you carry, the more creatinine you make, so a muscular person can sit naturally higher and someone with less muscle naturally lower — which is why the result is read together with your age and sex. Creatinine is also the number your GP uses to work out your eGFR (estimated glomerular filtration rate — a calculated estimate of how much blood your kidneys filter each minute).
Why is it tested?
A creatinine test is a standard part of checking kidney function, usually alongside urea, electrolytes and eGFR. Your GP may order it routinely, to look into symptoms such as tiredness or swelling, to keep an eye on a known kidney condition, or before and after starting medicines that the kidneys clear from the body. A single reading is only a snapshot, so the trend across several tests tells a clearer story than any one result — which matters most for picking up early changes, since these often cause no symptoms at all.
Reference range (Australia)
These are the Australasian Harmonised Reference Intervals endorsed by the AACB and the RCPA. Men generally sit higher than women because they tend to carry more muscle. The harmonised interval applies to adults up to age 60; for older adults laboratories may keep the same range. Always use the interval printed on your own report, which is already adjusted for sex.
Reference intervals vary between laboratories. Always use the range printed on your own report.
What your result means
A lower-than-usual creatinine is rarely a worry. It most often simply reflects having less muscle — common with age, in women, in pregnancy, or with reduced mobility. Less commonly it can go alongside significant liver disease or a low protein intake. Your GP reads it in the context of the rest of your results rather than on its own.
A creatinine within the range on your report suggests your kidneys are clearing this waste at the expected rate. Kidney health is supported by the everyday things — staying well hydrated, keeping blood pressure in a healthy range, and a balanced diet — and your GP can check in again over time or if your circumstances change.
A higher-than-usual creatinine can mean your kidneys are filtering a little less effectively than expected. But on its own it is not the whole story. Dehydration, a recent intense workout, a high-protein diet or creatine supplements, and some medicines can all push it up temporarily, and a naturally muscular build sits higher to begin with. Kidney filtering also tends to ease off gradually with age, which your GP factors in when reading an older adult's result, so a modestly raised creatinine is not automatically a sign of disease. A creatinine that is rising over time matters more than a single mildly raised reading. Your GP will look at it next to your eGFR and urea, ask about your fluids, exercise and medicines, and decide whether a repeat test or further checks make sense.
What can affect your result
A few things move creatinine without your kidneys necessarily changing. Muscle is the big one: more muscle means more creatinine, so athletes and very muscular people can read higher, while people with low muscle mass read lower. A hard or unaccustomed workout can lift it for a day or two, and so can a high-protein diet or creatine supplements. Dehydration concentrates it; rehydrating brings it back down. Several medicines also affect it. ACE inhibitors and ARBs (common blood-pressure medicines), NSAIDs (anti-inflammatory painkillers such as ibuprofen) and SGLT2 inhibitors (a type of diabetes medicine) can all change kidney filtering and shift the number. Because the kidney- function estimate calculated from creatinine can be imprecise in any one person, your GP weighs your result against your history, your other kidney markers and the medicines you take.
When to act
If your creatinine sits outside the range on your report, that is worth a conversation with your GP rather than a cause for alarm. A mildly raised result often just needs a repeat test to rule out temporary causes like dehydration, a recent workout or a new medicine, and to see whether it is steady or changing. A creatinine that climbs over time can point to declining kidney function, and may lead your GP to check your eGFR and urine, review your medicines, or refer you to a kidney specialist (nephrologist). This page is general information and is not a substitute for advice from your GP.
Frequently asked questions
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