What Is a Creatinine Blood Test? Results, Normal Ranges & What They Mean

Written by Dr. Simon Khela MBChB MRCGP, GMC Registered Doctor

Last reviewed: 30-07-2026

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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.

Why Do Doctors Request a Creatinine Blood Test?

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:

• Routine health screening, particularly if you are over 40, have high blood pressure, have diabetes, or have a family history of kidney disease
• Monitoring long-term conditions: both high blood pressure (hypertension) and type 2 diabetes are leading causes of chronic kidney disease, and creatinine is checked regularly in patients with either
• Before or during medication: certain medicines, including NSAIDs (such as ibuprofen), ACE inhibitors, metformin, and some antibiotics and chemotherapy drugs, are processed by the kidneys and require regular monitoring
• Before imaging with contrast dye: iodinated contrast used in CT scans depends on healthy kidneys to clear it safely from the body
• Investigating symptoms: persistent tiredness, swelling in the legs or ankles, changes in urination frequency, foamy or blood-tinged urine, or unexplained itching can all indicate kidney problems worth investigating
• Preoperative assessment: kidney function is routinely checked before planned surgery

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.

What Is Creatinine and Where Does It Come From?

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.

What Is a Normal Creatinine Level? UK Reference Ranges

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.

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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.

What Affects Creatinine Levels Besides Kidney Health?

Several factors unrelated to kidney disease can shift a creatinine reading up or down. Understanding these helps avoid unnecessary anxiety over a single result.

Muscle mass

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.

Diet — particularly red meat

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.

Dehydration

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.

Physical exercise

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.

Medications

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.

What Does a High Creatinine Level Mean?

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.

Chronic kidney disease (CKD)

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)

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.

Urinary tract obstruction

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.

Reduced blood flow to the kidneys

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.

What Does a Low Creatinine Level Mean?

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:

• Low muscle mass — most common in older adults, people of smaller build, or those who are largely sedentary
• Pregnancy — increased blood volume dilutes creatinine, and glomerular filtration rate rises substantially during pregnancy, leading to lower serum creatinine levels than in non-pregnant adults
• Very low protein diet — since dietary creatine (from meat and fish) contributes to creatinine production, a strict plant-based or very low-protein diet can reduce levels
• Advanced liver disease — the liver plays a role in creatine synthesis, so severe liver impairment can reduce creatinine production. In this context, low creatinine alongside abnormal liver function tests may prompt further investigation
• Muscle-wasting conditions — including muscular dystrophy, prolonged immobility, or malnutrition, which reduce the body’s total creatinine-producing muscle

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.

Creatinine and eGFR — How They Work Together

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.

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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 — What It Is and When It Is Used

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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.

Creatinine clearance normal range

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.

Creatinine clearance formula (Cockcroft-Gault equation)

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 creatinine clearance is preferred over eGFR

• Medication dose calculation, particularly for drugs where the creatinine clearance method (Cockcroft-Gault) is specified in the drug licence
• Pregnancy: eGFR formulae are less reliable in pregnancy; creatinine clearance from a 24-hour urine collection is more accurate
• Unusual body composition: very high or very low muscle mass, where standard eGFR formulae may be misleading
• Rapidly changing kidney function in acute settings where a more precise, real-time measure is needed

Albumin:Creatinine Ratio (ACR) — The Urine Companion Test

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.

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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.

What to Do Before a Creatinine Blood Test

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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:

• Avoid a large, protein-rich meal, particularly red or processed meat  in the two to three hours before the test. Cooked meat contains creatinine and creatine that is absorbed during digestion and can temporarily raise your result
• Try to avoid intense exercise in the 24 to 48 hours before the test. Strenuous physical activity temporarily increases creatinine production from muscle breakdown
• Stay well-hydrated on the day of the test. Dehydration concentrates blood and can cause a temporary rise in creatinine that resolves with adequate fluid intake
• Tell your GP, nurse or phlebotomist about any medications you take regularly  including over-the-counter pain relief (such as ibuprofen or naproxen), herbal supplements, and any recent changes to your prescriptions, as several drugs affect creatinine readings
• If you are collecting a 24-hour urine sample for creatinine clearance, follow the instructions provided exactly  collection must begin after the first void of the day, and all urine must be collected over a complete 24-hour period

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.

When Should You See a Doctor About Your Creatinine Result?

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:

• Persistent or unexplained tiredness or difficulty concentrating
• Swelling around the ankles, legs or eyes (oedema)
• Changes in urination — needing to go more frequently, especially at night (nocturia), or producing less urine than usual
• Foamy urine — which can indicate protein in the urine (proteinuria)
• Blood-tinged urine (haematuria)
• Persistent itching without a skin cause
• Nausea, poor appetite or unexplained weight loss
• High blood pressure that is difficult to control

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 , Bournemouth , Manchester and Cambridge.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.

The Bottom Line

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.

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Frequently Asked Questions About Creatinine Blood Tests