What Is Creatinine—And What Can Creatinine Levels Reveal?
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Medically reviewed by Femi Aremu, PharmD
Creatinine is a waste material your muscles produce as part of their everyday use. The kidneys then work to get rid of the substance. If your kidneys aren’t working properly, creatinine won't be eliminated through your urine and will instead build up in your bloodstream.
Abnormal levels of creatinine in your blood or urine may be a sign that your kidneys are not working properly, potentially due to kidney disease. Blood and urine tests can both measure your levels of creatinine and help determine whether you have any kidney problems.
Why Would Creatinine Levels Be Tested?
A creatinine test is one of several ways healthcare providers check your kidney function. The measurement can inform your healthcare provider how quickly and efficiently your kidneys are filtering and removing creatinine.
The most common reason that creatinine levels are checked is if you are showing signs of kidney disease. Kidney disease may have few or no symptoms in its very early stages. Common signs of later-stage kidney disease are:
Puffiness around your eyes, especially in the morning
Swollen feet and ankles
Trouble concentrating
Trouble sleeping
Muscle cramps at night
Dry, itchy skin
Your healthcare team might also test your creatinine levels if you have been diagnosed with a condition that may increase your risk of kidney disease. These conditions include:
They may also want to test your creatinine levels if you have a family history of kidney disease.
What Are Normal Creatinine Levels?
There are two ways that creatinine levels are measured: through your blood and urine. The results are presented in different values for each test. Normal ranges can differ slightly from lab to lab. Your healthcare provider can determine whether your results fall within the normal range for you.
Blood Test
The amount of creatinine in your blood that's considered normal is different for men and women. A normal level of creatinine in the blood for men is 0.7-1.2 milligrams per deciliter (mg/dL). For women, the normal amount is 0.5-1.0 mg/dL.
Besides your sex, your age and muscle mass might play a factor in what a normal level of creatinine in your blood should be for you.
Urine Test
A creatinine urine test is done over the course of a day. A normal level of creatinine can range anywhere from 500 to 2000 total milligrams (mg) in that day. What's considered normal for you will depend on how old you are and how much lean body mass you have.
Taking body mass into account, a normal daily level of creatinine is 14-26 mg per kilogram of body mass for men and 11-20 mg per kilogram of body mass for women.
What Does It Mean When Your Creatinine Is High?
When your blood creatinine levels are high, it may indicate that your kidneys aren't working the way they should and aren’t able to clear the naturally occurring creatinine out of your body. This could happen for a number of reasons.
Kidney disease is the most frequent reason why creatinine levels are high. Kidney disease is a condition that happens when your kidneys become damaged and are no longer able to properly eliminate waste, such as creatinine. It’s usually a progressive condition, meaning that it tends to get worse over time. If untreated, kidney disease can lead to kidney failure or cardiovascular disease.
Other possible reasons the creatinine levels in your blood may be high include the following conditions that can affect kidney function:
Bacterial kidney infection
Blocked urinary tract
Complication of diabetes
What Does It Mean When Your Creatinine Is Low?
Low levels of creatinine in your urine can be an indication of kidney disease or a condition that affects kidney function, such as an autoimmune disease or bacterial kidney infection. Low levels of creatinine in your urine means that the creatinine is staying in your body and not being properly filtered out by the kidneys.
When it comes to creatinine levels in your blood, it’s less common for creatinine to be low than it is for it to be high. Possible causes of low creatinine in the blood include:
Reduction in muscle bulk
Malnutrition
Liver disease
Substantial fluid overload
Augmented renal clearance, when the kidneys clear waste faster than normal
Research also suggests that low blood creatinine may be a predictor of poorer outcomes among people on dialysis or who are critically ill in the intensive care unit.
How to Prepare and What to Expect
Your healthcare provider will give you specific instructions for how to prepare for a blood or urine creatinine test. Usually, providers will ask you to refrain from eating cooked meat for 24 hours before your test. This is because consuming cooked meat can temporarily raise your creatinine levels. If you're taking a urine test, they may also ask you to stop taking certain medications that can alter results.
Here’s what to expect from the test themselves:
Blood Test
Getting a creatinine blood tests will be similar to any standard blood test. A healthcare provider will use a small needle to draw blood from one of the veins in your arm. You will be asked to sit still and try to relax as the blood is drawn. It’s common to feel a pinch or sting as the needle is inserted. The blood draw will only take a minute or two. Afterward, your arm may feel sore and may become bruised in the area where the blood was drawn.
A creatinine blood test is usually completed as part of a routine comprehensive metabolic panel or alongside a blood urea nitrogen (BUN) test, which measures a different waste product your kidney should be removing.
Urine Test
Creatinine urine tests usually require you to collect your urine over a 24-hour period so a fuller snapshot of your urine creatinine levels can be assessed. Your provider will give you a small urine collection container, along with instructions on how to best collect your urine in the container.
Usually, your first morning urine sample will not be used. But every time you urinate after that, you will be asked to collect a sample and record the time the sample was taken. You’ll need to store your samples in a refrigerator and deliver the sample to your provider or lab at the time that you were instructed to do so.
Factors That Could Influence Your Results
Abnormal creatinine levels could indicate some type of kidney dysfunction. But sometimes less serious factors may influence your results.
For example, if you are dehydrated, you may have abnormally high creatinine. Studies have found that eating cooked meat can cause temporary creatinine elevations. High-intensity exercise, such as resistance training, can also cause creatinine to become unusually high. Sometimes pregnancy can cause creatinine levels to be higher than normal. Finally, certain medications can cause creatinine level irregularities.
Related Tests and Measurements
If your healthcare provider suspects your kidneys aren’t performing normally, checking your creatinine levels will likely be one of several tests that need to be carried out. Here are some other possible tests your provider may order.
Creatinine Clearance Test
A creatinine clearance test compares the levels of creatinine in your blood and the creatinine levels in your urine. To do this, the test requires both a blood and urine sample. A creatinine clearance test may provide a more comprehensive view of your creatinine levels than either a urine or blood test in isolation.
A creatinine clearance test is measured as milliliters per minute (mL/min) or milliliters per second. A normal creatinine clearance is 97-137 mL/min for men and 88-128 mL/min for women.
GFR/eGFR Test
The glomerular filtration rate (GFR) is a blood measurement used to diagnose kidney disease in its earlier stages, as well as monitor people already diagnosed with kidney disease. The measurement is taken to see how well your kidneys' tiny filters (glomeruli) are functioning.
GFR may be considered a better indicator of kidney disease than a creatinine test alone because GFR takes into account your age, gender, race, and weight on top of your creatinine.
More often, providers will measure estimated GRF (eGFR) since the measurement is easier and less expensive to calculate than a GFR.
An eGFR of 90 or more is typically considered normal. If your score is between 60-89, you may be in the early stages of kidney disease, and if your score is between 15-59, you may have kidney disease. eGFR scores of less than 15 may indicate that you have kidney failure.
Other Tests
Other tests your healthcare provider may use to gauge the health of your kidneys include:
Blood pressure, as high blood pressure can cause kidney disease
Imaging tests to look the structure of your kidneys and how they function
A kidney biopsy to check for damage
A Quick Review
You naturally produce creatinine, a type of waste, each time you use your muscles. Most times, the kidneys are able to filter and eliminate excess creatinine from the body. When creatinine isn’t eliminated from your body, blood and urine tests will show that you have abnormal levels of creatinine. Creatinine levels that are too low or high could indicate your kidneys are not functioning well. This poor functioning could be because of kidney disease or a condition that affects kidney function, like an autoimmune disease. However, an abnormal creatinine level doesn’t always mean kidney disease, as levels can be altered by less serious factors like eating cooked meat, being dehydration, or exercising intensely. A healthcare provider can interpret your test results and determine whether other tests are needed before making any type of diagnosis.
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