Creatinine: Blood test, normal range, and how to lower levels

What is creatinine? | Good creatinine level | How to prepare for creatinine testing | Abnormal creatinine levels | How to lower creatinine levels | How to increase creatinine levels

You’re 10 minutes into your afternoon jog, powering through your daily exercise routine, or biking around the neighborhood. 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 exercising, 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 mainly synthesized in the kidneys, pancreas, and liver. Creatine is transported via blood flow to the skeletal muscles where it is stored in free and phosphorylated forms. However, creatine is mainly stored in its phosphorylated form, known as phosphocreatine or creatine phosphate. During exertion, your muscles convert the stored creatine molecules into energy, which assists in muscle contraction. After being used for energy, creatine is broken down into creatinine, which re-enters the bloodstream en route to the kidneys. 

Creatinine is released from the muscles and enters the bloodstream to be filtered at a relatively constant rate. 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, healthcare providers 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?

Creatinine levels are measured in milligrams per deciliter (mg/dL). In most cases, the normal range for serum creatinine (found in the blood) for someone with healthy kidneys is 0.7 to 1.3 mg/dL for adult males and 0.6 to 1.1 mg/dL for adult females.

However, there are a lot of variables when it comes to normal 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 blood test

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 a creatinine blood test to measure your serum creatinine levels, which can be used to estimate your glomerular filtration rate (GFR). Measuring GFR levels is vital in diagnosing kidney failure or chronic kidney disease. Your GFR can be measured directly, but the test can be complex and lengthy. Instead, healthcare providers can estimate GFR using serum creatinine levels. To calculate your estimated GFR (eGFR), healthcare providers will also take into account other factors, such as: 

• Age
• Gender
• Weight
• Height
• Race

​Creatinine urine test

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 over a 24-hour period to accurately assess kidney function. 

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. 

Creatinine clearance

Healthcare providers may order both tests as a way to measure your creatinine clearance, which refers to how well the kidneys filter creatinine from the blood into the urine. By comparing creatinine levels in the blood to the creatinine levels in the urine over the same 24-hour period, healthcare providers can get a comprehensive look at your kidney function. 

Blood urea nitrogen (BUN)

If your healthcare provider suspects kidney disease or damage, they may 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.

How to prepare for creatinine testing

Creatinine tests do not generally require any extensive preparation. However, depending on the test, your healthcare provider may recommend preparing in certain ways to ensure an accurate result. For example, you may be asked to refrain from eating cooked meat, such as beef, for 24 hours before a blood creatinine test. You may also be recommended to avoid strenuous exercise for two days before getting a creatinine test. Eating meat and vigorously exercising may increase your levels of creatinine. 

If you’re getting a creatinine urine test, you should stay hydrated and drink plenty of fluids over the 24-hour testing period. Make sure to use the container your healthcare provider gives you and follow their instructions to collect your urine over 24 hours. You may be asked to store the collected urine in the refrigerator and return the container with urine to your healthcare provider as instructed. 

You should also tell your healthcare provider about any medications you may be taking, including prescription drugs, over-the-counter medicine, and herbal supplements. Certain medications can alter creatinine levels and lead to inaccurate creatinine test results. These medications include:

• Bactrim (sulfamethoxazole/trimethoprim)
• Cephalosporin antibiotics, including Keflex (cephalexin), Ceftin (cefuroxime), and Ceclor (cefaclor)
• H2 antagonists, such as Zantac (ranitidine) and Tagamet (cimetidine)
• Nonsteroidal anti-inflammatory drugs (NSAIDs), including Aleve (naproxen) and Advil (ibuprofen)
• Fibrates, such as Tricor (fenofibrate)

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 (0.7 to 1.3 mg/dL for adult males and 0.6 to 1.1 mg/dL for adult females) may cause a healthcare provider to investigate further, but doesn’t always spell danger. Numerous factors can influence creatinine 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 may increase the production of creatinine.
• Increased protein consumption: Cooked meats contain creatinine, so if you’re eating steak and roast chicken every night, you could see higher levels. 

• Dehydration: Dehydration can lead to increased creatinine levels in the urine. In severe cases, dehydration can cause kidney damage.

• Certain medications: Sometimes, drugs can be the culprit. Some antibiotics, such as trimethoprim, and certain heartburn medications, such as cimetidine,can inhibit creatinine secretion. Sometimes, nonsteroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen, can also cause high creatinine levels.

• Pregnancy: During pregnancy, increased blood flow to the kidneys can lead to lower serum creatinine levels. However, in pregnant women with high blood pressure (preeclampsia), the kidneys may become damaged, leading to higher levels of serum creatinine. 

In some cases, higher-than-normal creatinine levels can indicate a serious health problem. Examples of medical conditions associated with high creatinine levels include:

• Kidney problems: High creatinine levels may be an indicator of chronic kidney disease, kidney infections, or acute kidney failure.
• Urinary tract blockage: If you can’t urinate, your body can’t eliminate creatinine. Kidney stones or other urinary disruptions may allow creatinine to remain in your bloodstream.
• Cardiovascular problems: Studies have shown that hypertension, heart failure, and other heart conditions may lead to increased creatinine levels.
• Autoimmune diseases: Some autoimmune diseases can affect the kidneys. For example, lupus is an autoimmune disease that can damage the kidneys, which can lead to increased creatinine levels.
• Diabetic kidney disease: Diabetes can lead to different complications, including kidney disease. Diabetic kidney disease may result in high creatinine levels. 

What level of creatinine indicates kidney failure?

A creatinine level of more than 1.4 for men and more than 1.2 for women may indicate that there is something wrong with the kidneys. If creatinine levels are higher than normal, a healthcare provider may recommend other tests to assess the problem. 

Measuring GFR can help confirm a problem with the kidneys. A GFR of 60 or more typically suggests normal kidney function, while a GFR of less than 60 usually indicates kidney disease. If you have kidney disease, your healthcare provider may recommend treatment options. A GFR of less than 15 could indicate kidney failure, which will likely require dialysis or a kidney transplant.  

In addition, a test may be recommended to check BUN levels. The normal range of BUN levels is from 7 to 20. Higher BUN levels than normal may indicate kidney disease or, in severe cases, kidney failure.

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

• Creatine supplements or other fitness supplements
• High-sodium processed foods
• Smoking
• Excessive alcohol consumption
• Overuse of NSAIDs

Natural remedies

• Chitosan supplements have shown a positive effect on renal health
• Salvia is a traditional Chinese medication for kidney disease
• Green tea may have beneficial effects on kidney disease and creatinine levels. In addition, herbal teas—specifically stinging nettle, chamomile, ginseng, and dandelion root may be helpful
• Cinnamon has been shown to reduce high creatinine levels in rats with acute kidney failure

It’s important to consult a healthcare provider before using supplements or natural remedies to treat high creatinine levels, especially high levels associated with kidney disease. Some herbal supplements may interact with other medications you may be taking. 

Medications

There are no medications that specifically reduce the amount of creatinine in your blood. If your healthcare provider determines kidney disease is causing abnormal creatinine levels, they might prescribe certain medications. Prescription drugs for kidney disease may include:

• Angiotensin-converting enzyme (ACE) inhibitors: Zestril (lisinopril), Lotensin (benazepril), and Capoten (captopril) are examples of ACE inhibitors that can lower high blood pressure and reduce pressure on the blood vessels in the kidneys.
• Angiotensin II receptor blockers (ARBs): Cozaar (losartan) and Avapro (irbesartan) are examples of ARBs that treat high blood pressure and have protective effects on the kidneys.
• Erythropoiesis-stimulating agents (ESAs): ESAs can help treat anemia (low red blood cells) caused by chronic kidney disease. Examples of ESAs that can help increase red blood cell counts include Procrit (epoetin alfa) and Aranesp (darbepoetin alfa).
• Phosphate or potassium binders: People with kidney disease may be unable to filter and excrete certain substances from the body. Phosphate or potassium binders can help eliminate extra phosphate and potassium that the kidneys are unable to filter. Phosphate binders include Renvela (sevelamer carbonate) and Fosrenol (lanthanum carbonate), while potassium binders include sodium polystyrene sulfonate and calcium polystyrene sulfonate.  

RELATED: Lotensin details | Captopril details

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What happens when creatinine levels are low?

Low creatinine isn’t always dangerous. It could be the result of normal aging or more serious conditions, such as liver disease. If your healthcare provider suspects low creatinine levels, they may run a serum creatinine test and evaluate what may be causing low creatinine levels. The main causes of low creatinine levels include:

• Decreased muscle mass: Creatinine production is directly related to muscle mass or how much muscle a person has. Aging and some health conditions, such as muscular dystrophy, can cause the muscles to deteriorate, leading to low creatinine levels. While low creatinine levels due to age are not usually a serious concern, low creatinine levels due to muscular dystrophy may warrant the need for treatment. Symptoms of low creatinine due to decreased muscle mass may include muscle weakness and trouble exercising.

• Liver problems: As much of the creatine in the body is produced in the liver, problems with the liver could lead to low creatinine levels. Symptoms may include nausea, pain in the upper right part of the abdomen, fatigue, and jaundice. 
• Malnutrition: Low creatinine may be caused by deficiencies in the diet. As creatine is primarily found in meat, people who are vegetarian may have lower levels of creatine than people who eat meat. In addition, people with low-protein diets or those who are unable to eat enough protein may also have low creatinine levels. Symptoms may include fatigue and weight loss. 
• Pregnancy: Low creatinine levels are often a normal part of pregnancy. Low creatinine levels should resolve after giving birth. 

How to increase creatinine levels

There are a number of ways to increase creatinine levels. Lifestyle changes are the main ways to increase creatinine levels. However, low creatinine levels may be a sign of an underlying problem. In many cases, treating low creatinine levels means treating other problems first.

• Eat more protein-rich foods: Eating more protein-rich foods can help increase creatinine levels. Protein-rich foods include meat, fish, and dairy products. The highest amounts of creatine are found in fish and red meats. 
• Exercise regularly: Creatinine is a by-product of creatine, which is used by the muscles for energy during exercise. Regular exercise at a moderate to high intensity can also help build and maintain muscle mass to improve creatinine levels. 
• Treat the underlying disease: If low creatinine levels are caused by an underlying condition, such as liver disease, treatment may be needed. 
• Creatine supplements: Creatine is one of the most studied supplements for exercise performance and muscle growth. Research suggests that creatine is a generally safe supplement that comes in different forms. Always consult a healthcare provider for medical advice on using creatine for low creatinine levels. 

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. However, high or low creatinine on its own doesn’t necessarily mean you have cancer. Cancer may instead be more related to kidney disease than to creatinine levels alone. 

Some research suggests that cancer is more common in people with advanced chronic kidney disease. In addition, the risk of death from cancer may be higher in people with chronic kidney disease. Other factors may also play a role in how kidney disease can affect the risk of cancer, such as diabetes, obesity, and smoking. 

Caring for your kidneys

In the end, the best medical advice for optimizing kidney function is to live 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.”