Creatinine

What is creatinine?

Creatinine is a waste product generated continuously from the normal breakdown of creatine phosphate in muscle tissue. It is produced at a relatively constant rate that depends primarily on muscle mass — which is why men, who generally have more muscle than women, have higher creatinine levels, and why athletes with significant lean mass may have naturally higher creatinine without any kidney problem.

The kidneys filter creatinine from the blood at the glomeruli and excrete it in urine. Because this filtration is continuous and the production rate is relatively stable, blood creatinine levels are an effective indicator of how well the kidneys are performing their filtration function. When kidney function declines — whether due to acute kidney injury or chronic kidney disease — creatinine accumulates in the blood, and its concentration rises.

In clinical practice, raw serum creatinine is routinely used to calculate the estimated glomerular filtration rate (eGFR) — a more clinically informative measure that estimates how many millilitres of blood the kidneys filter per minute per 1.73m² of body surface area, adjusted for age and sex. eGFR is a more consistent measure than creatinine alone because it corrects for the variation in creatinine production related to age, sex, and body size.

Creatinine is typically reported alongside urea, electrolytes (sodium, potassium), bicarbonate, and sometimes urate as part of a renal profile. Together, these markers provide a comprehensive picture of kidney function, electrolyte balance, and acid-base status.

Normal reference range

• Adult males: 60–110 µmol/L
• Adult females: 45–90 µmol/L
• eGFR (normal kidney function): above 90 mL/min/1.73m²
• eGFR indicating CKD (if persistent >3 months): below 60 mL/min/1.73m²

Important: Reference ranges vary between laboratories and depend on individual factors including age, sex, pregnancy status, and medication. Always interpret your result in the context of a clinician review. The Vesey reviews every result before release.

What high creatinine may indicate

Creatinine above the upper reference limit suggests reduced kidney filtration capacity. Important causes include:

• Chronic kidney disease (CKD) — progressive loss of nephrons from hypertension, diabetes, glomerulonephritis, or polycystic kidney disease; CKD is staged by eGFR and urine albumin-creatinine ratio
• Acute kidney injury (AKI) — sudden deterioration in kidney function from dehydration, sepsis, obstruction, nephrotoxic drugs, or contrast agents
• Dehydration — reduced blood volume leads to pre-renal azotaemia with acutely elevated creatinine and urea; corrects rapidly with rehydration
• High muscle mass — bodybuilders and athletes may have naturally higher creatinine with preserved eGFR; creatine supplementation also raises creatinine transiently
• Medications — trimethoprim, cimetidine, and some NSAIDs raise creatinine by blocking its tubular secretion without truly reducing GFR
• Obstruction — urinary tract obstruction from kidney stones, enlarged prostate, or tumour backs up pressure to the kidneys, impairing filtration

What low creatinine may indicate

Creatinine below the lower reference limit is typically associated with reduced muscle mass and is seen in:

• Sarcopenia — age-related muscle loss in older adults
• Malnutrition and cachexia — significant muscle wasting from chronic illness, cancer, or severe dietary restriction
• Liver disease — the liver synthesises creatine, so severe hepatic disease reduces creatine (and therefore creatinine) production
• Pregnancy — physiological increase in GFR during pregnancy lowers creatinine; this is normal and expected

Get tested at The Vesey, Sutton Coldfield

Creatinine and eGFR are measured within the following panels at The Vesey Private Hospital:

• Kidney Health panel — creatinine, eGFR, urea, electrolytes, and urate
• Extended Kidney Health panel — comprehensive renal assessment including urine ACR
• Lifestyle Screen — broad health check including kidney function
• Advanced Health Panels — full marker profiling including renal profile

Results are reviewed by a clinician before secure release, typically within 24 hours. Appointments available Monday–Saturday.

Frequently asked questions

What is a normal creatinine level?

Normal creatinine is 60–110 µmol/L for adult males and 45–90 µmol/L for adult females. Levels are lower in women due to typically smaller muscle mass. Values rise naturally with age as kidney filtration capacity gradually declines.

What is eGFR and how does it relate to creatinine?

eGFR (estimated glomerular filtration rate) is calculated from creatinine, age, and sex using the CKD-EPI equation. It estimates kidney filtration capacity in mL/min/1.73m². An eGFR above 90 is normal. Below 60 on two measurements at least 3 months apart indicates CKD. eGFR is more clinically meaningful than raw creatinine because it corrects for age and muscle mass.

Does high creatinine always mean kidney disease?

Not necessarily. High muscle mass, dehydration, creatine supplementation, and certain medications can all raise creatinine without true kidney disease. A single elevated result should be interpreted in context and repeated if there is doubt. The eGFR and clinical picture together are more informative than creatinine alone.

What can I do to protect my kidneys?

Stay well hydrated, avoid excessive NSAID use, control blood pressure and blood sugar, do not smoke, and maintain a healthy weight. Hypertension and diabetes are the two leading causes of CKD and require active management. Regular kidney function monitoring is important if you have either condition.

Should I fast before a creatinine test?

Fasting is not required for a creatinine test specifically. However, it is often measured as part of a comprehensive panel that may include fasting glucose and cholesterol. Stay well hydrated before the test — dehydration can temporarily raise creatinine and give a misleadingly low eGFR.