Kidney function, creatinine levels, and what your blood test result really tells you
Written by Trevor Sebuliba, Advanced Nurse Practitioner, BSc, MSc, NMP · Reviewed 2026
Seeing "HIGH" next to creatinine on your blood results can be alarming. Creatinine is one of the key markers your GP uses to assess kidney health, and a raised level is always worth understanding. This guide explains what creatinine is, what causes it to rise, and what a high result means for you.
Creatinine is a waste product produced naturally when your muscles break down a compound called creatine — an energy source used by muscle cells. Your kidneys filter creatinine out of the blood and excrete it in urine at a fairly constant rate. Because its production is relatively stable (depending on your muscle mass), the amount of creatinine in your blood reflects how efficiently your kidneys are clearing it.
When the kidneys are working well, creatinine levels remain within a predictable range. When kidney function falls, creatinine accumulates in the blood and the measured level rises.
| Group | Normal Range (µmol/L) |
|---|---|
| Adult male | 59 – 104 µmol/L |
| Adult female | 45 – 84 µmol/L |
| Older adults (65+) | Slightly higher upper limits are common |
| Children | Lower than adult ranges — varies by age |
Reference ranges vary between laboratories, so always compare your result against the reference interval printed on your own report.
A raised creatinine level — above the reference range for your age and sex — suggests that your kidneys are not clearing waste as efficiently as expected. However, it is important to interpret creatinine alongside other tests, particularly eGFR (estimated glomerular filtration rate) and urine tests. Creatinine alone does not give the full picture.
Reduced kidney function (chronic kidney disease): The most common reason for a persistently elevated creatinine is chronic kidney disease (CKD). CKD may be caused by diabetes, high blood pressure, recurrent kidney infections, certain autoimmune conditions, or inherited disorders such as polycystic kidney disease.
Dehydration: If you were poorly hydrated before your blood test, creatinine levels can appear falsely elevated. This is one of the most common reasons for a mildly raised result, particularly in otherwise healthy people. Your doctor may simply ask you to repeat the test having drunk normally beforehand.
Acute kidney injury (AKI): A sudden sharp rise in creatinine — particularly if you have recently been unwell, vomiting, on NSAIDs (such as ibuprofen), or been through surgery — may indicate acute kidney injury. AKI is a medical emergency and requires prompt assessment.
High muscle mass or strenuous exercise: Very muscular individuals naturally produce more creatinine. Intense exercise before a blood test can also temporarily raise levels. Creatine supplement use has a similar effect.
High meat intake: Consuming large amounts of meat (especially cooked red meat) in the 24 hours before a blood test can slightly elevate creatinine because dietary creatine from meat is converted to creatinine.
Certain medications: Some drugs — including trimethoprim (an antibiotic), cimetidine, and certain diabetes medications — can raise creatinine readings without reflecting true kidney damage. Your GP will take your medication list into account.
Your laboratory will often calculate an eGFR (estimated glomerular filtration rate) from your creatinine, age, and sex. eGFR is expressed in mL/min/1.73m² and directly estimates how much blood your kidneys are filtering per minute. For most adults, an eGFR above 90 is normal. CKD is classified into stages (G1–G5) based on eGFR.
| eGFR (mL/min/1.73m²) | CKD Stage | Kidney Function |
|---|---|---|
| 90 or above | G1 (if other markers present) | Normal or high |
| 60 – 89 | G2 | Mildly reduced |
| 45 – 59 | G3a | Mildly to moderately reduced |
| 30 – 44 | G3b | Moderately to severely reduced |
| 15 – 29 | G4 | Severely reduced |
| Below 15 | G5 | Kidney failure |
A result that is persistently elevated over two or more tests (separated by at least 3 months), combined with a low eGFR or protein in the urine, is more significant and warrants further investigation including urine tests (ACR — albumin-to-creatinine ratio), blood pressure monitoring, and possibly an ultrasound of the kidneys.
If you have a high creatinine or early CKD, the following steps can help slow any progression. Staying well-hydrated is important — aim for 6 to 8 glasses of fluid daily unless your doctor advises otherwise. Controlling blood pressure is one of the most important interventions, as hypertension is a major driver of kidney damage. If you have diabetes, tight blood sugar control slows kidney decline. Avoid regular use of non-steroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen and naproxen, as these reduce blood flow to the kidneys. Quit smoking if relevant, as smoking accelerates kidney disease progression. A diet lower in salt and processed foods reduces blood pressure. Your GP may also consider medications such as ACE inhibitors or SGLT2 inhibitors, which have proven kidney-protective effects.
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