Creatinine Blood Test: Normal Ranges, Causes & What Your Results Mean

What Is Creatinine?

Creatinine is a waste product generated by the normal breakdown of creatine phosphate in skeletal muscle. It is produced at a fairly constant rate, filtered out of the blood by the kidneys, and excreted in urine. Because the kidneys are responsible for clearing creatinine, its blood concentration serves as one of the most reliable markers of kidney function.

Unlike many blood markers that fluctuate with diet or stress, creatinine production is relatively stable day to day, making it an excellent baseline indicator. However, it is influenced by muscle mass — a bodybuilder will naturally have higher creatinine than a sedentary elderly person, even with identical kidney function.

Serum creatinine is almost always interpreted alongside the estimated glomerular filtration rate (eGFR), which adjusts for age, sex, and ethnicity to give a more accurate picture of how well your kidneys are filtering.

Why Is Creatinine Tested?

• Kidney function screening — creatinine is part of every standard renal panel and is the foundation for calculating eGFR
• Chronic kidney disease (CKD) monitoring — serial creatinine measurements track disease progression through CKD stages 1–5
• Medication safety — drugs like metformin, ACE inhibitors, and NSAIDs require kidney function checks before prescribing
• Pre-surgical assessment — anaesthetists check kidney function to adjust drug dosing
• Dehydration assessment — acute rises in creatinine can signal dehydration or reduced blood flow to the kidneys
• Diabetes management — diabetic nephropathy is a leading cause of CKD, making regular creatinine monitoring essential

Normal Ranges

Ranges vary slightly between laboratories. Muscular individuals may have levels at the upper end of normal without any kidney impairment.

What Do High Creatinine Levels Mean?

• Chronic kidney disease — the most common clinical cause; creatinine rises as kidney filtration declines
• Acute kidney injury (AKI) — sudden creatinine spikes indicate rapid loss of kidney function from dehydration, sepsis, or drug toxicity
• Dehydration — reduced blood volume concentrates creatinine
• High protein diet — excessive meat consumption can transiently raise creatinine
• Creatine supplements — creatine monohydrate is metabolised to creatinine, raising blood levels without indicating kidney damage
• Rhabdomyolysis — massive muscle breakdown floods the blood with creatinine and myoglobin
• Medications — trimethoprim and cimetidine inhibit tubular secretion of creatinine, raising levels without affecting true kidney function
• Heart failure — reduced cardiac output decreases renal perfusion

What Do Low Creatinine Levels Mean?

• Low muscle mass — elderly, malnourished, or bed-bound patients produce less creatinine
• Liver disease — the liver synthesises creatine; severe liver disease reduces creatinine production
• Pregnancy — increased blood volume and renal blood flow lower creatinine in the second and third trimesters
• Overhydration — dilution effect from excessive fluid intake
• Muscle-wasting conditions — muscular dystrophy, myasthenia gravis, and prolonged corticosteroid use

How to Improve Your Creatinine Levels

• Stay well hydrated — adequate water intake supports kidney filtration without overloading
• Moderate protein intake — if creatinine is high, consider reducing red meat and supplementing with plant-based protein sources
• Review supplements — if you take creatine monohydrate, discuss with your doctor whether it is affecting your results
• Manage blood pressure — hypertension is a leading cause of kidney damage; target <140/90 mmHg or as advised by your GP
• Control blood sugar — keeping HbA1c below 48 mmol/mol (6.5%) protects kidney function in diabetes
• Avoid nephrotoxic drugs — limit NSAID use and discuss alternatives with your prescriber
• Exercise regularly — moderate exercise supports cardiovascular and renal health, but avoid extreme exertion if kidney function is compromised

When Should You Get Tested?

• You have diabetes, hypertension, or a family history of kidney disease
• You are taking medications that affect kidney function (metformin, ACE inhibitors, NSAIDs)
• You experience symptoms like swollen ankles, fatigue, changes in urination, or foamy urine
• You are over 60 — NHS Health Checks include kidney function screening
• You want a baseline kidney function measurement as part of a wellness check

Which Lola Health Tests Include Creatinine?

Creatinine is included in our Core Health panel alongside eGFR, urea, and electrolytes for a complete kidney function assessment. It is also part of Peak Insights and Vital Check. Available as an individual add-on with any Lola Health blood test.