← All Tests
Kidney Test

Creatinine Test

Creatinine is the key marker of kidney function. High creatinine means your kidneys are struggling to filter waste. Here's exactly what your number means.

Written and clinically reviewed by Suman Konda, PharmD, Clinical Pharmacist · Based on peer-reviewed sources · Editorial policy · Not medical advice

Last reviewed and updated: · How we check our content

What is Creatinine?

Creatinine is a waste product produced by muscle metabolism. Healthy kidneys filter creatinine out of the blood and excrete it in urine. When kidneys are damaged or stressed, creatinine builds up in the blood: causing blood creatinine levels to rise. Creatinine is the most commonly tested kidney marker and is part of the standard KFT (Kidney Function Test) panel.

Creatinine Normal Range

GroupNormal Range (mg/dL)
Men0.74 – 1.35
Women0.59 – 1.04
Children (2–12 yrs)0.3 – 0.7
Elderly (>60 yrs)Slightly lower (less muscle mass)
Creatinine Test: reference intervals by group (mg/dL)A bar for each group showing its reference interval on a shared scale. The same figures appear in the table above.0.190.510.821.141.46Men0.74–1.35Women0.59–1.04Children (2–12 yrs)0.3–0.7mg/dL
Creatinine Test: reference intervals by group (mg/dL), drawn from the table above. Intervals differ between laboratories: compare your result against the range printed on your own report.

Why a Normal Creatinine Can Still Hide Kidney Trouble

Creatinine is a waste product of muscle. Your muscles produce it continuously at a rate that depends mainly on how much muscle you have, and your kidneys clear it. That makes it a useful marker of kidney function, but it also means the number carries information about your body as well as your kidneys, and the two are easy to confuse.

The consequence is uncomfortable but important. Two people can have identical kidney function and quite different creatinine results simply because one carries more muscle. A muscular young man may sit above the quoted range with entirely healthy kidneys. A frail, elderly or very slight person — or someone who has lost muscle through illness — may produce so little creatinine that their result looks reassuringly normal while their kidneys are working at a fraction of capacity.

The group this misleads most oftenOlder adults with low muscle mass. Their creatinine can sit comfortably inside the reference range while their filtration rate is genuinely reduced. This is precisely why kidney function is reported as an eGFR, which adjusts for age and sex, rather than left as a raw creatinine for you to compare against a range.

When eGFR Itself Is Uncertain

Because eGFR is calculated from creatinine, it inherits creatinine’s dependence on muscle. Estimates built on creatinine alone are imprecise, and that imprecision can push people into a chronic kidney disease label they do not merit.2

There is a second marker, cystatin C, which the body produces largely independently of muscle mass. Combining the two gives a more accurate estimate than either alone. In the study that established the combined equation, the improvement was largest exactly where it matters most — among people whose creatinine-based eGFR sat in the borderline range. Of those with an estimate between 45 and 59, adding cystatin C correctly reclassified about 17% as actually having a filtration rate of 60 or above, meaning they did not have the reduced kidney function the first test implied.2

The ratio between the two markers is itself informative, and is used as an indirect indicator of muscle mass, which is why a discrepancy between them tends to say something about body composition rather than about the kidneys.3

Worth asking aboutIf you have been told your eGFR is borderline — particularly if you are older, have little muscle, are a serious athlete, or the result does not fit how you feel — it is reasonable to ask whether a cystatin C test would clarify it before a chronic kidney disease label is applied. It is a confirmatory test, not a replacement.

Two other things move creatinine without any change in kidney function. A large meat meal raises it for several hours, and heavy exercise shortly before the blood draw does the same. If a single unexpected result is the only abnormality, repeating it under ordinary conditions is often the first sensible step.

What does HIGH creatinine mean?

HIGH Creatinine above 1.4 mg/dL (men) / 1.1 mg/dL (women)

High creatinine (hypercreatininaemia) means the kidneys are not filtering efficiently. Common causes: dehydration (most common, drink more water and retest), chronic kidney disease (CKD from diabetes or hypertension), acute kidney injury (from infection, medication, contrast dye), kidney stones blocking urinary flow, or high muscle mass / high protein diet (minor effect). Always repeat the test after good hydration before concluding kidney disease.

Creatinine above 2.0 mg/dL: Significant kidney impairment

Creatinine above 2 mg/dL usually indicates at least 50% loss of kidney function. Your doctor will calculate eGFR (estimated Glomerular Filtration Rate) which is more accurate than creatinine alone. At this level, kidney ultrasound, urine protein and nephrology referral are typically needed.

What is eGFR and why does it matter more than creatinine?

eGFR: the real measure of kidney function

eGFR (estimated GFR) is calculated from creatinine, age, sex and race. It estimates what percentage of normal kidney function you have. Most labs now report eGFR alongside creatinine.

eGFR (mL/min/1.73m²)CKD StageMeaning
>90G1 (normal)Normal kidney function
60–89G2Mildly reduced
30–59G3Moderately reduced
15–29G4Severely reduced
<15G5Kidney failure: dialysis territory

Questions to ask your doctor

  • Could dehydration explain my high creatinine? Should I retest after drinking more water?
  • What is my eGFR and what stage of CKD does that represent?
  • Should I reduce protein intake or avoid NSAIDs (ibuprofen)?
  • Do I need to see a nephrologist?

Frequently asked questions

What is worth asking a doctor about an abnormal Creatinine?
Whether it needs repeating, whether a medicine or recent illness explains it, how far outside the range it actually falls, and whether it changes management or simply needs watching. Those four questions cover most of what matters.
Is a slightly abnormal Creatinine a reason to worry?
Rarely on its own. Reference intervals are built to contain the middle 95% of a healthy population, so mild deviations are common in well people. The size of the deviation, its direction over time and your symptoms decide whether it means anything.
Does Creatinine need to be measured fasting?
That depends on the rest of the panel. Samples are usually drawn together and the fasting rule is set by the strictest test included, not by Creatinine alone. Follow whatever instruction you were given when the test was arranged.

References

The clinical information on this page is drawn from peer-reviewed sources indexed by the US National Library of Medicine. Links go to the source so you can read it yourself.

  1. Renal Function Tests. In: StatPearls. Treasure Island (FL): StatPearls Publishing. NCBI Bookshelf NBK507821
  2. Creatinine Clearance. In: StatPearls. Treasure Island (FL): StatPearls Publishing. NCBI Bookshelf NBK544228
  3. Inker LA, Schmid CH, Tighiouart H, et al. Estimating glomerular filtration rate from serum creatinine and cystatin C. N Engl J Med. 2012;367(1):20–9. PMID 22762315 · doi:10.1056/NEJMoa1114248
  4. Rizk JG, Streja E, Wenziger C, et al. Serum creatinine-to-cystatin-C ratio as a potential muscle mass surrogate and racial differences in mortality. J Ren Nutr. 2022;33(1):69–77. PMID 34923112 · doi:10.1053/j.jrn.2021.11.005

Related reading

Medical Disclaimer: This page is for general educational purposes only. It does not constitute medical advice. Always consult a qualified doctor before making any health decisions.