A creatinine blood test measures the level of creatinine — a waste product produced continuously by muscle activity — in your blood. Because healthy kidneys filter creatinine from the bloodstream at a constant rate and excrete it in urine, a raised serum creatinine level is one of the most reliable early indicators that kidney function may be impaired. In the UK, a normal serum creatinine level is approximately 60–110 micromoles per litre (μmol/L) for adult men and 45–90 μmol/L for adult women, though reference ranges vary between laboratories.
This guide explains what a creatinine blood test involves, how to read your result, what normal looks like for UK adults, and what raised or low levels can indicate — so you have a clear picture whether you are preparing for a test or reviewing your results. If you would like to discuss your result with a doctor, you can book a private blood test or a private GP appointment at any of our eight UK clinics.
Creatinine is one of the most commonly ordered kidney function tests in both NHS and private practice. Your GP might request one for several reasons:
Creatinine is almost always reported alongside eGFR (estimated glomerular filtration rate), a calculated value that converts your creatinine result into an estimate of how much blood your kidneys filter per minute. Together, serum creatinine and eGFR give a far clearer picture of kidney health than either marker alone. Creatinine is also often tested alongside blood urea nitrogen (BUN), another waste product filtered by the kidneys, and the two together help distinguish between different causes of abnormal results.
Creatinine is the breakdown product of creatine phosphate, a compound stored in muscle tissue and used as a rapid energy source during physical activity. As muscles contract and creatine is metabolised, creatinine is produced as a byproduct and released into the bloodstream. Unlike many other waste products, creatinine is generated at an almost constant rate throughout the day, proportional to an individual's muscle mass.
The kidneys remove creatinine from the blood through the glomeruli tiny filtration units and excrete it in urine. Because production is constant and healthy kidneys clear it efficiently, blood creatinine levels remain stable under normal circumstances. When the kidneys' filtering capacity is reduced, creatinine accumulates in the blood, which is why it is such a useful clinical marker.
The terms serum creatinine and blood creatinine refer to the same measurement of creatinine in a sample of blood serum rather than in whole blood or urine. When your lab report says creatinine, it means serum creatinine unless specifically stated otherwise.
Creatinine is measured in micromoles per litre (μmol/L) in the United Kingdom. US laboratory reports use milligrams per decilitre (mg/dL); these are different units and should not be compared directly with UK figures.
Your individual lab report will state the reference range used for your specific sample and method. A result just outside the printed range does not automatically indicate a problem. Context matters: a GP will consider your eGFR, your symptoms, your medication history, your level of hydration on the day, and your recent activity before drawing conclusions.
Several factors unrelated to kidney disease can shift a creatinine reading up or down. Understanding these helps avoid unnecessary anxiety over a single result.
Creatinine production is directly proportional to muscle mass. Bodybuilders, athletes, and people with larger or more muscular builds will naturally produce more creatinine and therefore run higher baseline levels. Conversely, elderly individuals, those with muscle-wasting conditions, or people who are of smaller build will typically produce less. This is one reason eGFR calculations include age and sex as variables.
Cooked meat contains preformed creatinine and creatine that is absorbed during digestion. A large, meat-heavy meal in the two to three hours before a blood test can temporarily raise your creatinine reading. This effect is short-lived, but for the most accurate result, it is worth avoiding a heavy meat-based meal immediately before testing.
When fluid intake is low, blood becomes more concentrated, and waste products including creatinine rise proportionally. A temporarily raised creatinine result that resolves after rehydration is not a sign of kidney disease — but your GP may want to repeat the test after a period of adequate fluid intake to confirm the result. Exercising without adequate hydration, or being unwell with vomiting or diarrhoea, can also cause a temporary rise.
Intense exercise — particularly in the 24 to 48 hours before a blood test — increases creatinine production as muscles work harder and break down more creatine. Endurance athletes and people who have recently done heavy resistance training may see a temporary rise that does not reflect kidney function.
Several commonly prescribed drugs are known to affect creatinine levels. Trimethoprim (an antibiotic) and cimetidine (an antacid) interfere with the way the kidneys secrete creatinine, raising blood levels without any change in actual kidney function. NSAIDs (including ibuprofen and naproxen), ACE inhibitors, angiotensin receptor blockers, and certain chemotherapy agents can all affect creatinine by changing blood flow to the kidneys. Always tell your GP or phlebotomist about your regular medications before a creatinine blood test.
A raised serum creatinine level — above approximately 110 μmol/L in men or 90 μmol/L in women — suggests the kidneys may not be filtering waste from the blood as efficiently as usual. The causes range from entirely benign and temporary to conditions requiring prompt investigation.
CKD is the most common reason for persistently elevated creatinine in adults. It develops gradually, often over years, and is most commonly caused by long-standing high blood pressure or type 2 diabetes. In early CKD, there may be no symptoms at all — the raised creatinine and reduced eGFR are discovered incidentally on a routine blood test. CKD is staged from G1 (normal or high eGFR ≥90 with kidney damage markers) to G5 (kidney failure, eGFR <15), and ongoing monitoring of creatinine and eGFR tracks how function is changing over time.
Acute kidney injury (AKI) is a sudden, significant drop in kidney function that develops over hours to days. AKI causes a rapid rise in creatinine and requires urgent assessment. Common triggers include severe dehydration, serious infection or sepsis, certain nephrotoxic medications (such as NSAIDs, aminoglycoside antibiotics, or contrast dye given to patients with vulnerable kidneys), major surgery, or a significant drop in blood pressure. AKI is reversible if identified and treated quickly, but it can cause permanent kidney damage if left untreated.
A blockage preventing urine from draining normally such as kidney stones, an enlarged prostate, or a tumour, causes waste products including creatinine to accumulate. The kidneys continue producing urine but cannot expel it effectively. An ultrasound scan of the kidneys and bladder is often requested if obstruction is suspected.
The kidneys require an adequate blood supply to filter waste. Conditions that reduce renal perfusion including symptoms of a heart attack, severe haemorrhage, or significant blood pressure drops can cause creatinine to rise. This is sometimes described as pre-renal acute kidney injury and typically improves when the underlying cause is treated.
A single raised creatinine reading is not a diagnosis. Your GP will usually repeat the test, check your eGFR, and consider your symptoms and history before making any decisions. If kidney disease is suspected, further investigations may follow, including an albumin: creatinine ratio (ACR) urine test, a blood pressure check, and an ultrasound scan. A referral to a nephrologist (kidney specialist) may be offered if results are significantly abnormal or declining.
Low creatinine below approximately 60 μmol/L in men or 45 μmol/L in women is much less commonly a cause for concern than a raised result. The most frequent explanations are:
In most cases, low creatinine on its own requires no treatment. Your GP will interpret it in the context of your overall results, symptoms and history. Isolated low creatinine in a healthy, active adult with a normal eGFR is rarely clinically significant.
eGFR (estimated glomerular filtration rate) is calculated directly from your serum creatinine result, combined with your age and sex. It estimates how much blood your kidneys are filtering each minute — expressed in millilitres per minute per 1.73 m² (mL/min/1.73m²). Because eGFR is derived from creatinine, the two values move in opposite directions: as creatinine rises, eGFR falls, and vice versa.
The NICE chronic kidney disease guideline (NG203) defines CKD as an eGFR below 60 mL/min/1.73m² sustained for more than three months, or an eGFR above 60 alongside other markers of kidney damage such as proteinuria. A single low reading is not sufficient for a CKD diagnosis — GPs look for a pattern across at least two readings separated by at least 90 days before concluding that function is genuinely reduced.
eGFR calculations assume stable, steady-state creatinine levels. They are not valid if creatinine is changing rapidly, such as in acute kidney injury, and can underestimate kidney function in people with very high muscle mass (such as bodybuilders) or overestimate it in those with very low muscle mass.
Creatinine clearance is a direct measure of how efficiently the kidneys are removing creatinine from the blood, expressed in millilitres per minute (mL/min). Unlike eGFR, which is estimated from a formula applied to a single blood test, creatinine clearance is traditionally measured using both a serum creatinine blood test and a 24-hour urine collection — the patient collects all urine passed over a full 24-hour period, and the concentration of creatinine in the sample is measured and combined with the blood result.
Normal creatinine clearance is approximately 90–130 mL/min for adult men and 80–120 mL/min for adult women. These values decline with age as kidney function naturally reduces.
The most widely used formula for estimating creatinine clearance from a blood test alone (without a urine collection) is the Cockcroft-Gault equation:
Creatinine clearance (mL/min) = [(140 − age) × weight in kg] ÷ [serum creatinine in μmol/L × 0.815]
(For women, the result is multiplied by 0.85 to account for lower average muscle mass.)
This formula is particularly important in clinical pharmacology — it is used to calculate safe drug doses for medicines excreted by the kidneys, including many antibiotics, anticoagulants, and chemotherapy agents. When your doctor is adjusting a medication dose based on your kidney function, they are usually using creatinine clearance rather than eGFR.
When a creatinine blood test shows reduced kidney function, or when your GP suspects kidney damage even with a normal creatinine, a urine test for the albumin:creatinine ratio (ACR) is usually ordered alongside or shortly after. The ACR measures how much albumin (a protein) is leaking from the blood into the urine — a sign that the kidneys' filtering membranes are damaged.
Under the NICE CKD guideline (NG203), both eGFR stage and ACR category are used together to determine CKD stage and guide management decisions. A persistently elevated ACR alongside a reduced eGFR significantly increases the risk of CKD progression and cardiovascular disease.
Blood urea nitrogen (BUN) is another kidney waste marker that is often checked alongside creatinine. The BUN:creatinine ratio can help distinguish between different causes of raised creatinine — for example, a high ratio may suggest pre-renal causes (such as dehydration or reduced blood flow to the kidneys), while a normal ratio is more consistent with intrinsic kidney disease.
No special preparation is required for a routine creatinine blood test. There is no need to fast, and you can take your usual medications unless your GP tells you otherwise. However, the following can help ensure your result is as accurate as possible:
The blood draw itself takes only a few minutes. A small sample is taken from a vein in your arm. At a private Medical clinic, results are typically available within 24 to 48 hours.
You do not need to wait for a blood test to prompt a GP appointment if you are experiencing symptoms that could relate to kidney function. Symptoms worth raising with a doctor include:
These symptoms have many possible causes beyond kidney problems, but they are worth raising at a GP appointment rather than waiting for a routine check-up. If you already have a blood test result you are uncertain about, a GP can explain what your specific figures mean, arrange any necessary follow-up tests, and refer you to a nephrologist if appropriate.
We offer same-day private GP appointments and private blood testing across all eight of our UK clinics — in London, Birmingham, Newcastle, Leicester, Oxford, Derby, Sutton Coldfield and Bournemouth. Full pricing is available on our fees page. Our GMC-registered GPs can talk through your creatinine result and arrange any follow-up tests during a single consultation.
A creatinine blood test is a simple, well-established way to monitor kidney health. Mildly abnormal results are common and often explained by dehydration, a meat-heavy meal, intense exercise, or a temporary illness — rather than kidney disease. That said, no blood test result should be read in isolation. Serum creatinine needs to be interpreted alongside eGFR, the albumin:creatinine ratio, your symptoms, your medications and your medical history by a qualified clinician.
If you have a result you are not sure about, our GMC-registered GP team is available to talk it through with you at a private appointment, with same-day availability at our UK clinics.
A creatinine blood test measures the level of creatinine — a waste product from muscle metabolism — in your blood. Because healthy kidneys filter creatinine continuously at a constant rate, a raised level indicates that kidney filtration may be impaired. Normal serum creatinine in the UK is approximately 60–110 μmol/L for adult men and 45–90 μmol/L for adult women.
Creatinine is a marker of how well your kidneys are filtering waste from the blood. A raised result suggests reduced kidney function and is interpreted alongside eGFR (estimated glomerular filtration rate), which converts your creatinine level into an estimate of how many millilitres of blood your kidneys filter per minute. The two figures together give a much clearer picture of kidney health than creatinine alone.
A raised creatinine level — above approximately 110 μmol/L in men or 90 μmol/L in women — suggests the kidneys may not be filtering waste effectively. The most common causes are chronic kidney disease (often driven by high blood pressure or diabetes), acute kidney injury, dehydration, a urinary tract obstruction, or the effect of certain medications. A single raised result is not a diagnosis — a GP will repeat the test, check eGFR, and consider your symptoms and history before drawing conclusions.
Low creatinine most commonly reflects lower muscle mass — common in older adults, people of smaller build, or during pregnancy. It can also occur with a very low protein diet or, rarely, with muscle-wasting conditions or advanced liver disease. Low creatinine in isolation is rarely a cause for concern, but your GP will review it alongside your other results.
Normal serum creatinine ranges in the UK are approximately 60–110 μmol/L for adult men and 45–90 μmol/L for adult women. Reference ranges can vary slightly between laboratories and testing methods. A result just outside these ranges does not necessarily indicate a problem without considering eGFR, muscle mass, hydration and other factors.
Creatinine clearance measures how much creatinine the kidneys remove from the blood each minute. It can be calculated using both a blood and a 24-hour urine sample, or estimated using the Cockcroft-Gault formula from a blood test alone. Normal creatinine clearance is approximately 90–130 mL/min for men and 80–120 mL/min for women. It is particularly used in medication dose calculations and during pregnancy, where standard eGFR formulae are less reliable.
The ACR is a urine test that measures how much albumin (a protein) is leaking from the blood into the urine — a sign that the kidneys' filtering membranes may be damaged. A normal ACR is below 3 mg/mmol. Values of 3–30 indicate mildly increased albuminuria, and above 30 indicates significant proteinuria. Together with eGFR, ACR is used to stage chronic kidney disease under the NICE CKD guideline (NG203).
Yes. Dehydration concentrates the blood, which can temporarily raise your creatinine reading even when your kidneys are working normally. Drinking adequate water and retesting after rehydration often brings the level back within range. Your GP may ask you to repeat the test if dehydration is a likely explanation for a mildly raised result.
In μmol/L, a creatinine level of 100 falls within the typical range for adult men (60–110 μmol/L) but above the typical range for adult women (45–90 μmol/L). Whether it requires action depends on the eGFR result calculated alongside it, your muscle mass, hydration, recent diet and exercise, and any symptoms. A GP would assess all these factors before deciding whether further tests are needed.
Yes, particularly when the cause is temporary — such as dehydration, a recent high-protein meal, or intense exercise, all of which resolve without treatment. Where creatinine is raised due to an underlying condition such as CKD, levels can often be stabilised with appropriate management of blood pressure, blood sugar and other risk factors, as set out in the NICE CKD guideline (NG203). In acute kidney injury, creatinine may return to baseline once the trigger is treated.
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