Creatinine is a waste product your muscles produce as they use energy, and it shows up on blood tests because it’s one of the most reliable indicators of how well your kidneys are working. Your body generates creatinine at a fairly steady rate throughout the day, and healthy kidneys filter nearly all of it out of your blood and into your urine. When your kidneys lose filtering ability, creatinine builds up in your bloodstream, so a higher-than-normal level on a blood test can be an early signal of kidney trouble.
Where Creatinine Comes From
Your muscles store a compound called creatine, which they burn for quick energy. As that energy gets used, creatine breaks down into creatinine and enters your bloodstream. Most creatinine production happens in skeletal muscle, which is why the amount circulating in your blood is closely tied to how much muscle mass you carry. A larger, more muscular person will naturally produce more creatinine than someone with a smaller frame.
Creatinine also comes, to a lesser extent, from the meat you eat. Cooked meat contains creatine that your body converts the same way. Under normal circumstances, though, your production rate stays remarkably consistent from day to day, which is exactly what makes it useful as a kidney marker. If the amount being made holds steady but the amount in your blood starts climbing, the problem is almost certainly on the filtering side.
Why Kidneys and Creatinine Are Linked
Your kidneys filter blood through tiny clusters of blood vessels called glomeruli. Creatinine passes freely through these filters. The kidneys don’t reabsorb it or break it down further. They simply move it into urine. About 15% of the creatinine in your urine actually gets there through a second route: active secretion by the kidney’s tubules. When kidney function starts declining, that secretion pathway picks up some of the slack, which means creatinine levels in your blood can stay deceptively normal in the early stages of kidney disease.
This is one reason a single creatinine reading doesn’t tell the whole story. Your lab report will typically include a calculated number called the estimated glomerular filtration rate, or eGFR, which gives a clearer picture.
What eGFR Means on Your Report
Rather than interpreting your creatinine number in isolation, labs plug it into a formula along with your age and sex to estimate how much blood your kidneys filter per minute. This result is your eGFR, measured in milliliters per minute. An eGFR of 60 or above is generally considered normal. A score below 60 suggests kidney disease, and the lower the number, the more advanced the disease.
The current standard formula, recommended by the National Kidney Foundation, no longer includes a race variable. It was updated in 2021 to improve accuracy across populations. Your lab should be using this newer calculation automatically.
One important nuance: because creatinine production depends on muscle mass, eGFR calculations based solely on creatinine can overestimate kidney function in people with very low muscle mass and underestimate it in people who are exceptionally muscular. In situations where creatinine alone isn’t accurate enough, labs can measure a second marker called cystatin C. Using both markers together produces a more reliable estimate of kidney function than either one alone.
Normal Creatinine Ranges
Reference ranges vary slightly between labs, but typical values for adults fall roughly between 0.7 and 1.3 mg/dL for men and 0.6 and 1.1 mg/dL for women. The difference reflects the fact that men, on average, carry more muscle mass. These ranges are guidelines, not hard cutoffs. A creatinine level that’s technically “in range” but has risen significantly compared to your previous results still warrants attention.
Context matters more than any single number. Your results should be compared against your own baseline over time, not just against a population average.
What High Creatinine Can Mean
An elevated creatinine level most commonly points to reduced kidney function. That can range from mild, early-stage chronic kidney disease (which often has no symptoms at all) to more serious conditions like kidney failure. Specific causes include poor blood flow to the kidneys, a blockage in the urinary tract, kidney infection, or damage from long-standing conditions like diabetes or heart failure. Diabetic kidney disease is one of the most common reasons for a gradually rising creatinine level.
But high creatinine doesn’t automatically mean your kidneys are in trouble. Several non-kidney factors can push the number up temporarily:
- Intense exercise: A hard workout in the day or two before your blood draw can spike creatinine, especially if it involved significant muscle strain.
- High meat intake: Eating a large amount of cooked meat shortly before testing adds extra creatine to your system.
- Creatine supplements: Popular among athletes and gym-goers, these directly increase the raw material your body converts to creatinine.
- Dehydration: Less fluid in your blood concentrates everything, including creatinine.
- Certain medications: Some drugs interfere with creatinine secretion in the kidneys, raising blood levels without actually affecting kidney filtration.
- Muscle injury or breakdown: A condition called rhabdomyolysis, where muscle tissue breaks down rapidly, floods the blood with creatinine.
Because so many variables can influence the result, a single elevated reading usually prompts a repeat test or additional workup rather than an immediate diagnosis.
What Low Creatinine Can Mean
A creatinine level that’s lower than expected typically reflects reduced muscle mass rather than a kidney problem. This can happen with aging, prolonged bed rest, malnutrition, muscle-wasting diseases, or a history of amputation. Severe liver disease can also lower creatinine because the liver plays a role in producing creatine in the first place. Pregnancy commonly lowers creatinine levels because blood volume expands significantly, diluting the concentration.
People who follow a vegan or vegetarian diet tend to run lower because they’re not getting creatine from meat. This isn’t a health concern in itself, but it does mean their eGFR may appear higher than it truly is, potentially masking early kidney problems.
Factors That Can Skew Your Results
The National Kidney Foundation notes that the effect of outside factors on creatinine is “highly variable,” meaning two people eating the same steak dinner or taking the same supplement might see very different changes in their blood levels. Still, being aware of these influences helps you and your provider interpret results accurately.
Things that can make creatinine appear artificially high (and eGFR appear lower than reality): large amounts of cooked meat, creatine supplements, recent high-intensity exercise, very high muscle mass, and certain medications including some used in HIV treatment and some antibiotics.
Things that can make creatinine appear artificially low (and eGFR appear higher than reality): a plant-based diet, low muscle mass, pregnancy, severe liver disease, and muscle-wasting conditions.
If you know any of these apply to you, mention it when reviewing results with your provider. In some cases, confirming kidney function with cystatin C testing gives a more accurate answer. Research published in the American Journal of Kidney Diseases found that using both creatinine and cystatin C together improves risk prediction across all stages of kidney function, not just in borderline cases.
Preparing for a Creatinine Test
A creatinine blood test is a simple blood draw, usually done as part of a basic or comprehensive metabolic panel. Most labs don’t require fasting specifically for creatinine, though you may need to fast if other tests are being run at the same time. Avoiding an unusually large meat-heavy meal the night before and skipping intense exercise for 24 to 48 hours beforehand can help ensure your result reflects your true baseline rather than a temporary spike. If you take creatine supplements, let your provider know, as this is one of the most common non-medical causes of elevated readings.
Results are typically available within a day or two. If your creatinine or eGFR comes back outside the expected range, the next step is usually a repeat test to confirm the finding, along with a urine test to check for protein, which provides additional information about kidney health.