Creatinine Blood Test: Normal Levels, High, Low & eGFR

Creatinine is a waste product made by your muscles and cleared by your kidneys. Its blood level — reported on lab work as serum creatinine — is the most common marker of kidney function, because it is the number your lab feeds into the estimated glomerular filtration rate (eGFR). A high creatinine is alarming to see, but it does not always mean kidney disease. This guide explains what creatinine is, normal creatinine levels in mg/dL, what a high or low creatinine means, and — most importantly — how to read the eGFR, which is what clinicians actually act on. It is normally reported next to BUN, its partner kidney marker.

Key takeaways

• Creatinine comes from creatine breakdown in muscle and is filtered out by the kidneys, so its blood level tracks kidney filtration.¹
• Typical U.S. values: about 0.7–1.3 mg/dL (men) and 0.5–0.95 mg/dL (women) — but sources disagree on exact cutoffs, and the range depends on muscle mass and your lab's method.²³
• What matters clinically is the eGFR, now calculated with the race-free CKD-EPI 2021 equation: 90 or above is normal, below 60 for more than 3 months defines chronic kidney disease.⁴⁵⁶
• A high creatinine can reflect kidney injury but also high muscle mass, a meat-heavy meal, creatine, or medications that block secretion with no real drop in filtration; a low creatinine is usually benign; neither is a cancer marker.⁷³¹

What is creatinine?

Creatine supplies quick energy to muscle; as it breaks down, it produces creatinine, a waste product the blood carries to the kidneys for excretion in urine. Because production is fairly constant — proportional to your muscle mass — and the kidneys filter it continuously, the blood concentration mirrors filtration function: if the kidneys filter less well, creatinine accumulates and rises.³

That is why nobody stops at the raw number: your lab combines it with your age and sex to compute an estimated glomerular filtration rate (eGFR) in mL/min/1.73 m² — far more informative than creatinine alone, and read alongside albuminuria in a kidney work-up.⁸⁹

Creatinine is also secreted by the kidney tubules, not just filtered — which means creatinine-based clearance overestimates true GFR by roughly 10% to 20%.³ This guide covers serum creatinine in the blood; urine creatinine serves a different purpose.

Creatinine is almost never ordered alone: it comes in a basic metabolic panel (BMP) or comprehensive metabolic panel (CMP) — routine panels that also report glucose, electrolytes, calcium, and BUN — and reduced filtration often raises it alongside a high BUN and uric acid.¹⁰¹¹ Your PCP typically orders one at a checkup; if results point to kidney disease, you may be referred to a nephrologist.

Why creatinine is measured

Clinicians check creatinine to assess kidney function (at a checkup or to follow known disease), to monitor at-risk conditions like diabetes and high blood pressure, to adjust dosing of drugs cleared by the kidneys or clear a patient before contrast imaging, and to work up symptoms of kidney involvement.¹

This matters at scale: chronic kidney disease (CKD) affects more than 1 in 7 U.S. adults — an estimated 35.5 million Americans — and as many as 9 in 10 who have it are unaware. About 1 in 3 people with diabetes and 1 in 5 with high blood pressure have kidney disease.¹²

Normal creatinine levels

Below are typical adult reference values — they depend on sex, muscle mass, and your lab's method, so compare to the range printed on your report.

Creatinine values per MedlinePlus;² eGFR values per the National Kidney Foundation and Cleveland Clinic.⁴⁵

Sources genuinely disagree here — and you should know it. MedlinePlus gives 0.7–1.3 mg/dL (men) and 0.5–0.95 mg/dL (women).² StatPearls gives approximately 0.6–1.2 mg/dL (men) and 0.5–1.1 mg/dL (women).³ Cleveland Clinic's basic metabolic panel range is 0.58–0.96 mg/dL, with no split by sex.¹⁰ These are not contradictions but evidence that there is no single universal cutoff — reference intervals depend on the assay, the population, and the lab, which is why a result 0.05 mg/dL "over the line" means little on its own, and why the eGFR is what gets acted on.

A note on units. The U.S. reports creatinine in mg/dL; most of Europe, including France, uses µmol/L. To convert: µmol/L ÷ 88.4 = mg/dL, and mg/dL × 88.4 = µmol/L. So a European result of 106 µmol/L is 1.2 mg/dL — the same value in different clothing.

eGFR: the number that actually matters

The takeaway of this guide: creatinine alone is misleading, and eGFR is the fix. The estimated glomerular filtration rate estimates how many milliliters of blood your kidneys clear per minute, standardized to a body surface area of 1.73 m². It is reported automatically on most U.S. panels.

eGFR stages, per the National Kidney Foundation:⁴

Two clarifications. First, eGFR declines with age even without kidney disease: the NKF gives averages of 116 at ages 20–29, 107 at 30–39, 99 at 40–49, 93 at 50–59, 85 at 60–69, and 75 at 70+.⁴ Second, chronic kidney disease requires the eGFR to stay below 60 for three months — a single low reading is not a diagnosis — though you can also have CKD with an eGFR above 60 if there are other signs of kidney damage, such as albuminuria.⁵¹³

The race-free equation: what changed in 2021

Older eGFR equations included a race coefficient that mechanically raised estimated GFR for patients identified as Black — a practice with no defensible biological basis that could delay diagnosis and transplant access. In 2021, the National Kidney Foundation–American Society of Nephrology (NKF-ASN) Task Force on race in kidney diagnosis recommended abandoning it,⁶ and a new CKD-EPI 2021 equation was published that estimates GFR from creatinine without race.¹⁴

U.S. practice has followed: the NIDDK now recommends the CKD-EPI equations without a race coefficient — the 2021 creatinine and creatinine-cystatin C equations, and the 2012 cystatin C equation.⁸ StatPearls reflects the same standard.³ If your report is a few years old, it may still carry a race-based estimate — ask.

Beyond creatinine: cystatin C

Creatinine depends on muscle mass.¹⁵ When a precise GFR is needed — at the extremes of body composition, in frailty, or before dosing a narrow-margin drug — clinicians add cystatin C, a marker much less dependent on muscle. The NIDDK calls using both "more accurate than using serum creatinine alone."⁸¹⁴¹⁶

What a high creatinine means

A high creatinine (and the lower eGFR with it) means the kidneys are filtering less well — or that something else changed production or secretion. Main causes:⁷¹⁷²

• Chronic kidney disease — from diabetes, high blood pressure, and age — raising creatinine slowly, over years;¹²
• Acute kidney injury (AKI) — from dehydration, severe infection, low blood flow, or nephrotoxic drugs — raising it fast, over hours to days;¹⁷
• Dehydration, the most common benign explanation for a modestly high result;²
• High muscle mass, a recent red-meat meal, or creatine supplements — all of which raise creatinine without kidney injury (red meat by roughly 30%);³¹⁸
• Rhabdomyolysis — massive muscle breakdown from crush injury, extreme exertion, or certain drugs. It is "a major cause of AKI," with AKI risk estimated between 10% and 50% when CPK is greater than 1000 U/L;¹⁹
• Urinary obstruction — a downstream blockage (stones, enlarged prostate, tumor) backs pressure into the kidney;²
• Medications that block tubular secretion — notably trimethoprim (in trimethoprim–sulfamethoxazole) and cimetidine — which raise measured creatinine without any real fall in GFR (a "pseudo-elevation"). Trimethoprim–sulfamethoxazole can raise serum creatinine by about 15% to 22%.³²⁰

When should you worry? Not because of an isolated number. What counts is the eGFR, its trajectory, your albuminuria, and your context: a creatinine slightly over the line, stable for years, in a weightlifter differs from one that climbed 40% in a week or is paired with urine protein. A rapid rise or a low eGFR warrants medical attention — but not panic.

Creatinine is also a late marker: about 50% of kidney function must be lost before serum creatinine rises detectably.³ Reason to take a genuinely abnormal result seriously — and not over-read small wobbles inside the range.

Does high creatinine mean cancer? No. Creatinine reflects kidney filtration and muscle mass, not tumor activity — it is not a tumor marker. Some cancers or their treatments can affect the kidneys, but that is not what a routine high creatinine is announcing.

What a low creatinine means

A low creatinine gets far less attention than a high one, but it is a common result and a common question. It is usually not a cause for concern — MedlinePlus notes that "low levels of blood creatinine aren't common."¹ The explanations that matter:

• Low muscle mass. By far the leading cause. Creatinine is downstream of muscle: a slight build, advanced age, sarcopenia, prolonged bed rest, or an amputation all mean less creatine to break down and less creatinine to measure — the number is telling you about your muscles, not your kidneys.³¹⁵
• Pregnancy. Blood volume expands and GFR rises, so creatinine normally runs lower — expected physiology, not a problem.³
• Malnutrition or a low-protein diet. Undernutrition, an eating disorder, a low-protein or plant-forward diet, or starvation all reduce creatinine.³¹⁵
• Advanced liver disease. The liver synthesizes creatine, so serious liver disease can lower creatinine — MedlinePlus lists "serious liver disease" among the causes.¹
• Overhydration, which dilutes the measured concentration.

The clinically important trap: a low creatinine can mask reduced kidney function — someone with very little muscle can produce so little that the number looks normal while true GFR is already impaired.¹⁵ Another case where cystatin C earns its keep.¹⁶ A low creatinine rarely needs treatment itself, but if it reflects malnutrition or muscle loss, that does.

The BUN/creatinine ratio

Because creatinine sits next to BUN on every basic panel, U.S. clinicians routinely read the BUN/creatinine ratio — BUN divided by creatinine, both in mg/dL, normally about 10:1 to 20:1.²¹ It is informative because the kidney handles the two molecules differently: creatinine is filtered and barely reabsorbed, while urea is partly reabsorbed — more so when the kidney is conserving water.

• Above ~20:1 — points to a prerenal cause: dehydration, blood loss, heart failure, low kidney perfusion. Gastrointestinal bleeding is the classic non-perfusion cause.
• Around 10:1–20:1 with both values rising together — points to intrinsic kidney disease.
• Below ~10:1 — suggests low protein intake, advanced liver disease, rhabdomyolysis (creatinine rises disproportionately), or dialysis.²¹

Two caveats: the 10:1 baseline holds best in moderate to advanced renal failure, and the ratio is useful but imperfect — BUN answers to diet, hydration, and liver function as much as to the kidney. It orients a work-up; it never closes one.²¹⁷

What can affect your creatinine

Beyond muscle mass, diet, hydration, medications, age, and pregnancy, creatine supplements deserve a note.³¹⁵ Creatine monohydrate raises serum creatinine by supplying more substrate; that elevation is not kidney damage. A 2023 narrative review and a widely cited Q&A review both find no evidence that creatine at recommended doses harms the kidneys in healthy people.¹⁸²² If your creatinine is high and you take creatine, say so — cystatin C can settle it.¹⁶

Recent research

According to recent PubMed publications:

• Updated benchmarks for kidney disease. The international KDIGO 2024 guideline stages chronic kidney disease on eGFR and albuminuria — the basis of diagnosis and follow-up.¹³ A large JAMA meta-analysis confirms that eGFR and albuminuria together predict adverse outcomes better than either alone,⁹ while reviews detail how muscle mass, nutrition, and drugs distort creatinine-based estimates — and when to reach for the more accurate creatinine + cystatin C combination.¹⁴⁶⁷¹⁵
• Protecting the kidneys: SGLT2 inhibitors. Major trials (DAPA-CKD, EMPA-KIDNEY) showed that SGLT2 inhibitors slow the progression of chronic kidney disease, with or without diabetes.²³²⁴ (eGFR decline served as a trial endpoint — e.g. NCT03036150.)²⁵

These findings concern monitoring and management; they do not justify self-medication or replace your physician's advice.

Get your creatinine interpreted by AI DiagMe

A creatinine is never read alone: its meaning depends on your eGFR, your muscle mass, your albuminuria, your medications, and how it has moved over time. That cross-referencing is what gives the result its real value.

👉 AI DiagMe interprets your lab results — blood, urine, or stool — in plain language, taking your whole profile into account. An informational service that does not provide a diagnosis and complements, never replaces, your physician.

Frequently asked questions

Bottom line

Creatinine is a muscle waste product filtered by the kidneys; its main job is to feed the eGFR, the real measure of kidney function. Keep the orders of magnitude in mind (men ~0.7–1.3 mg/dL, women ~0.5–0.95 mg/dL, with genuine disagreement between sources); a high creatinine is not a cancer sign and may come from muscle, meat, creatine, or medication, while a low creatinine usually points at your muscles. It is the eGFR — now race-free — its trend, and your albuminuria that say whether there's a problem. No single value is read alone: what matters is the full set of your markers and your profile — which is what AI DiagMe provides, alongside your physician.

Sources

Official sources and peer-reviewed publications (PubMed, ClinicalTrials.gov) used for this guide: