Elevated Creatinine Levels Explained
What high creatinine means in your blood test, why it happens, and what your GP will do next — written for Australian patients by health data analysts.
What Is Creatinine?
Creatinine is a waste product created by the normal breakdown of creatine phosphate in your muscles. Every time your muscles contract — walking, typing, breathing — they use creatine for energy and produce creatinine as a byproduct. Your kidneys filter creatinine from the blood and excrete it in urine.
In a healthy person, creatinine production and excretion are in balance. Your blood level stays relatively constant day to day. When your kidneys are not filtering effectively, creatinine builds up in the blood — which is why it is used as a marker for kidney function.
Normal Creatinine Ranges
Reference ranges vary slightly between Australian pathology labs. The ranges below are based on RCPA guidelines and are representative of most labs including Laverty, QML, Sullivan Nicolaides, and Melbourne Pathology.
Adult males
Higher muscle mass generally produces higher baseline creatinine.
Adult females
Lower range reflects typically lower muscle mass compared to males.
Children (1–12 years)
Increases gradually with age and body size.
Adolescents (12–18 years)
Approaches adult levels during puberty as muscle mass increases.
Elderly (>70 years)
Reduced muscle mass may mask declining kidney function. eGFR is more reliable.
Creatinine and eGFR — The Relationship
Your pathology report will almost always show both creatinine and eGFR (estimated glomerular filtration rate) together. eGFR is calculated from your creatinine using the CKD-EPI formula, which also factors in your age and sex. Australian labs adopted the race-neutral CKD-EPI 2021 equation.
The key insight: creatinine and eGFR move in opposite directions. As creatinine rises, eGFR falls. A creatinine of 150 µmol/L in a 60-year-old male might correspond to an eGFR of around 42 mL/min/1.73m² — placing them in CKD Stage 3b. The same creatinine in a 25-year-old muscular male might give an eGFR of 55, which is still reduced but less concerning.
eGFR is more clinically useful than raw creatinine because it accounts for body size and age. Your GP will primarily use eGFR when assessing kidney function and staging any kidney disease.
Common Causes of Elevated Creatinine
Not every high creatinine reading means kidney disease. Many causes are temporary and reversible.
Dehydration
The most common temporary cause. Reduced blood volume concentrates creatinine. Drinking adequate water before a retest often normalises levels. Australian summers make this especially relevant.
High muscle mass
Bodybuilders, athletes, and people with naturally large frames produce more creatinine. A muscular 90 kg male may have a creatinine of 115 µmol/L that is completely normal for them. Context matters.
High-protein diet
Eating large amounts of red meat or taking creatine supplements can temporarily raise creatinine by 10–20%. A cooked steak the night before your test will show up.
Intense exercise
Heavy weight training or endurance exercise within 24–48 hours breaks down muscle tissue and releases creatinine into the blood. Levels normalise within a few days.
Medications
ACE inhibitors, ARBs, NSAIDs (ibuprofen, naproxen), certain antibiotics (trimethoprim, gentamicin), and proton pump inhibitors can raise creatinine. Some raise it by blocking tubular secretion without actual kidney damage.
Acute kidney injury (AKI)
A sudden drop in kidney function from infection, blood loss, severe dehydration, or nephrotoxic drugs. Creatinine rises rapidly over days. This is a medical emergency requiring urgent treatment.
Chronic kidney disease (CKD)
The gradual, irreversible loss of kidney function over months to years. Often caused by diabetes, high blood pressure, or glomerulonephritis. The most clinically important cause of persistently elevated creatinine.
Urinary tract obstruction
Kidney stones, enlarged prostate, or tumours blocking urine flow. Back pressure on the kidneys reduces their ability to filter creatinine. Usually reversible once the obstruction is cleared.
CKD Staging — Where Do You Sit?
Chronic kidney disease is classified into 5 stages based on eGFR. This staging system, endorsed by Kidney Health Australia and the RCPA, guides clinical management decisions.
Stage 1
Normal kidney function with other signs of kidney damage (protein in urine, structural abnormality)
Action: Monitor annually. Manage blood pressure and diabetes if present.
Stage 2
Mildly reduced function. Often found incidentally on routine blood tests.
Action: Monitor 6–12 monthly. Investigate cause. Cardiovascular risk management.
Stage 3a
Mild to moderate reduction. Most patients are asymptomatic.
Action: Monitor 3–6 monthly. Consider nephrology referral. Adjust medication doses.
Stage 3b
Moderate to severe reduction. Some patients begin to develop symptoms (fatigue, fluid retention).
Action: Nephrology referral recommended. Active management of complications.
Stage 4
Severe reduction. Symptoms are common: fatigue, nausea, swelling, itch, poor appetite.
Action: Specialist care essential. Begin planning for dialysis or transplant.
Stage 5
Kidney failure. Kidneys can no longer sustain life without intervention.
Action: Dialysis or kidney transplant required. Urgent specialist management.
What Your GP Will Do Next
If your creatinine is elevated, your GP will follow a structured investigation pathway. Here is what to expect.
1. Repeat the test
A single elevated creatinine is NOT diagnostic. Your GP will almost always repeat the blood test in 1–4 weeks, ideally under controlled conditions (well hydrated, no intense exercise for 48 hours, fasting if requested). If the second result is normal, it was likely transient.
2. Calculate eGFR trend
Your GP will compare your current eGFR with previous results. A declining trend over 3+ months is more concerning than a single low reading. SmarterBlood tracks this automatically when you upload multiple blood tests.
3. Urine test (ACR)
An albumin-to-creatinine ratio (ACR) from a spot urine sample checks for protein leaking from the kidneys. Elevated ACR combined with reduced eGFR strongly suggests kidney disease. This is a simple urine test collected at the pathology lab.
4. Review medications
Your GP will check whether any of your current medications could be raising creatinine. Common culprits include NSAIDs, ACE inhibitors, ARBs, and certain antibiotics. Sometimes stopping or changing a medication is all that is needed.
5. Check blood pressure and glucose
High blood pressure and diabetes are the two leading causes of CKD in Australia. If either is uncontrolled, managing them aggressively is the most important step to protect kidney function.
6. Renal ultrasound
If kidney disease is suspected, an ultrasound checks kidney size, shape, and whether there is any obstruction. Small, shrunken kidneys suggest chronic disease. Obstruction (stones, enlarged prostate) is usually treatable.
7. Nephrology referral
Your GP will refer you to a nephrologist if eGFR is below 30, declining rapidly (>5 mL/min/year), or if the cause is unclear. In Australia, most nephrologists work through public hospital outpatient clinics with Medicare-covered consultations.
Frequently Asked Questions
Can drinking more water lower my creatinine?
If your elevated creatinine is caused by dehydration, then yes — rehydrating will bring it back to your baseline within 24–48 hours. However, if the elevation is due to kidney disease, drinking more water will not fix the underlying problem. Stay well hydrated, but do not try to flush your kidneys with excessive water intake.
Does a high creatinine always mean kidney disease?
No. High creatinine can be caused by dehydration, high muscle mass, intense exercise, high-protein meals, medications, or temporary illness. A single elevated result requires a repeat test. Only a persistent elevation over weeks to months, combined with reduced eGFR and/or proteinuria, points toward kidney disease.
What is the difference between creatinine and eGFR?
Creatinine is a raw measurement of a waste product in your blood. eGFR (estimated glomerular filtration rate) is a calculated value that uses your creatinine along with your age, sex, and sometimes ethnicity to estimate how well your kidneys are actually filtering. eGFR is more clinically useful because it accounts for the individual factors that affect creatinine levels.
My creatinine is 120 µmol/L. Should I be worried?
It depends on context. For a 25-year-old muscular male, 120 µmol/L might be normal. For a 70-year-old petite woman, it could indicate significant kidney impairment. Always look at eGFR alongside creatinine, and compare with your previous results. Your GP can interpret this in the context of your full health picture.
Is creatinine affected by fasting?
Creatinine itself is not significantly affected by fasting. However, hydration status matters — being dehydrated concentrates your blood and raises creatinine. Drink water normally before your test. A high-protein meal the night before can also mildly elevate creatinine.
How often should I have my creatinine checked?
For most healthy adults, creatinine is checked as part of routine blood work every 1–2 years. If you have diabetes, high blood pressure, heart disease, a family history of kidney disease, or are taking nephrotoxic medications, your GP may check it every 3–12 months depending on your risk level and any prior abnormal results.
Related Reading
Track Your Creatinine Over Time
Upload your blood test results and SmarterBlood will chart your creatinine and eGFR trends automatically — so you can see whether your kidney function is stable, improving, or declining.
This information is based on guidelines from the Royal College of Pathologists of Australasia (RCPA), Kidney Health Australia, and the Chronic Kidney Disease Management Handbook. Reference ranges may vary between pathology providers. SmarterBlood provides educational information only and is not a substitute for professional medical advice.