You’re on mile two of your afternoon run, or powering through a third set on the bench, or biking uphill on your daily commute. You’re breathing fast, and your muscles are on fire. Sweat drips off your chin. Heat flushes your cheeks. And when you’re done, nothing feels better than a warm shower, a cold glass of water, and a seat on the couch.
Like most people, you’re acutely aware of how physical activity makes your body feel—the breathing, sweat, and heat. You might even thrive on it. But there’s a whole lot more going on under the surface. When your muscles break down during exercise, they slowly build back up, increasing muscle mass, but this process also releases waste products into your blood, primarily creatinine.
While it might be the last thing you think about while you’re timing your miles or hitting a one-rep max, your blood creatinine levels can be a key indicator of your renal health and kidney function.
What is creatinine?
Everyone has certain serum creatinine levels in their bloodstream. Creatinine is a natural byproduct of muscle use, caused by the breakdown of a chemical called creatine. Creatinine itself doesn’t have a specific physiological function—it’s just a waste product. It simply stays in the blood until reaching the kidneys, where it’s filtered and eliminated through urination.
So, how does your body generate creatinine? It starts with creatine, which is synthesized in the kidneys, pancreas, and liver, then transported via blood flow and stored in your skeletal muscles. During exertion, your muscles convert creatine to energy, which assists in muscle contraction. After serving its purpose, creatine becomes creatinine and re-enters the bloodstream en route to the kidneys.
Even though creatinine doesn’t actively benefit (or harm) your body, the amount of creatinine in your blood can be measured to evaluate your kidney health. For this reason, physicians will often use a creatinine test—along with other lab tests, like a blood urea nitrogen (BUN) test—to monitor for chronic kidney disease (CKD) or renal failure.
What is a good creatinine level?
In most cases, the normal range for serum creatinine (found in the blood) for someone with healthy kidneys is 0.9 to 1.3 mg per deciliter for adult males and 0.6 to 1.1 mg per deciliter for adult females.
However, there are a lot of variables when it comes to levels of creatinine. “Normal” is a somewhat subjective term. Muscle breakdown creates creatinine, so your muscle mass and activity level can influence the amount in your blood. To accurately measure blood creatinine levels, a doctor will first assess these various factors to establish a baseline, according to Taylor Graber, MD, an anesthesiologist and founder of ASAP IVs. “Creatinine level assessment starts with getting a demographic baseline to assess what ‘normal levels’ should be,” Dr. Graber says. “This depends on age, race, gender, and body size. Once these values are normalized, changes from this range can signify abnormalities of the kidney.”
Healthcare providers like to keep an eye on creatinine levels for various reasons. If you had or currently have kidney disease, kidney damage, diabetes, or another illness that affects your kidneys, or are taking a medication that could affect your kidneys, your healthcare provider might order regular creatinine measurement to monitor your renal function. The most common test methods are via blood and urine.
Creatinine that comes from your blood is called serum creatinine, and it can be measured by administering a routine blood test. “When kidney function becomes impaired, less creatinine is able to be cleared, which results in a higher level of creatinine in the blood,” Dr. Graber explains. “While this test does not directly tell you how well the kidney is functioning, it can be followed over time for changes.” Healthcare providers can use this creatinine blood test (along with factors like age, sex, race, etc.) to calculate your glomerular filtration rate (GFR), which is vital in diagnosing kidney failure or chronic kidney disease.
The other most common way to test creatinine levels is through a 24-hour urine collection. Why 24 hours? Exercise, diet, and hydration can all affect creatinine, so your levels could fluctuate throughout the day. Therefore, your healthcare provider will need multiple urine samples to evaluate your creatinine clearance effectively. As you might imagine, this test involves collecting all of your urine over 24 hours, then delivering it to your healthcare provider. Based on the results, your healthcare provider can determine how well your kidneys are filtering creatinine into the urinary tract.
Healthcare providers will order both tests to get a comprehensive look at your kidney function by comparing your estimated GFR (eGFR) with the amount of urine creatinine present. If your doctor suspects kidney disease or damage, he or she may also order a blood urea nitrogen (BUN) test to confirm their diagnosis. This test measures the amount of urea nitrogen—another type of waste filtered by the kidneys—in a blood sample.
What do abnormal creatinine levels mean?
So, you went to the doctor, did the tests, and the results are in: You have high creatinine levels. Now what? Step one—don’t panic. Elevated creatinine doesn’t necessarily mean your kidneys are in a downward spiral. Anything outside the normal range (0.9 to 1.3 mg per deciliter for adult males and 0.6 to 1.1 mg per deciliter for adult females) may cause a healthcare provider to investigate further, but doesn’t always spell danger. Numerous factors can influence your test results. Here are just a few:
- Increased exercise: Have you been on a fitness kick? In the gym every day? This spike in muscle breakdown will increase the production of creatinine.
- Increased protein consumption: Cooked meats contain creatinine, so if you’re feasting on steak and roast chicken every night, you could see higher levels.
- Urinary tract blockage: If you can’t urinate, your body can’t eliminate creatinine, so kidney stones and other urinary disruptions will allow it to remain in your bloodstream.
- Certain medications: Sometimes, drugs can be the culprit. The antibiotic trimethoprim and Cimetidine, a stomach ulcer and heartburn medication, can inhibit creatinine secretion. Sometimes, non-steroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen, can also be a cause.
- High blood pressure: Studies have also shown that hypertension, heart failure, and other heart conditions can cause increased creatinine levels.
Likewise, low creatinine isn’t always dangerous. It could be the result of low muscle mass (or a muscle disease like muscular dystrophy), pregnancy, a low-protein diet, or certain liver conditions.
Can creatinine levels change quickly?
Creatinine levels can change rapidly, even throughout the day, which is why healthcare providers monitor them for an extended period of time. One blood test that returns high creatinine in blood could be a fluke. However, several tests in a row that show elevated levels could indicate chronic kidney disease. A sudden spike in creatinine levels could be a warning sign for acute kidney damage or other conditions, depending on symptoms.
What is the connection between cancer and creatinine levels?
Abnormal creatinine levels could also indicate kidney or prostate cancer. Although, high or low creatinine on its own doesn’t necessarily mean you have cancer.
How to lower creatinine levels
How your healthcare provider treats your abnormal creatinine levels depends entirely on the underlying cause. Changes in lifestyle and diet can be a simple and effective treatment for minor cases. But chronic kidney disease, kidney damage, or kidney failure require more robust procedures. Medications to control symptoms, dialysis, or in the most extreme cases, a kidney transplant may be necessary. Here are a few potential methods for lowering creatinine levels:
What to do
- Stay hydrated
- Reduce protein intake
- Reduce vigorous activity (but don’t cut out exercise altogether!)
- Get more fiber in your diet (specifically from fruits and vegetables)
What to avoid
There are no medications that specifically reduce the amount of creatinine in your blood. If a doctor determines kidney disease is causing abnormal creatinine levels, he or she might prescribe medication to alleviate symptoms. Prescription drugs include:
- Angiotensin-converting enzyme (ACE) inhibitors like Lotensin (benazepril) and Capoten (captopril) to lower high blood pressure.
- Angiotensin II Receptor Blockers (ARBs) like Edarbi (azilsartan) and Teveten (eprosartan) also treat high blood pressure and can reduce the amount of protein in your urine.
- Erythropoiesis-stimulating agents (ESAs) to help increase your red blood cell count.
- Phosphate or potassium binders to help eliminate extra phosphate and potassium that your kidneys can’t filter.
In the end, the best medical advice for optimizing kidney function is living a consistently healthy lifestyle. Dr. Graber says: “Minimizing unhealthy foods high in processed ingredients, increasing fruit and vegetable intake, regular exercise (150 minutes of moderate-intensity or 75 minutes of vigorous-intensity aerobic exercise per week), staying hydrated, and maintaining body weight in a healthy range (body mass index of 20 to 25) are things to focus on over time to make sure you are giving the body the tools it needs to be successful.”