Two letters can make a big difference — people often confuse creatinine with creatine. But the two are completely different substances. Creatine is a compound that can be found in supplements and some foods. It’s also found naturally in your muscles as well as your brain tissue and even in the testes (male reproductive organs). People who use creatine supplements often want to improve their athletic performance and build muscle.

What Is Creatinine?

When your body breaks down creatine, it makes a waste product called creatinine. Creatinine can be found in your blood and is released by your kidneys through urine. Creatinine primarily builds up in your blood as your body breaks down creatine in your muscles. To a lesser extent, your creatinine levels are also affected by the protein you eat.

Creatinine tests are used to diagnose kidney disease, monitor chronic conditions you might have, and see if the medications you’re taking are affecting your kidneys. Most of the time, creatinine tests are part of your normal blood work. But in some cases, they may be ordered if a problem is suspected.

Knowing what creatinine is, how your levels affect your kidneys, and what abnormal test results mean can be useful in helping you protect your kidney health. Here is what you need to know about creatinine, including which tests are used to measure it and when to talk to your healthcare provider.

What Factors Affect Creatinine Levels?

The amount of creatinine in your blood will vary from person to person and can be influenced by your age, sex, muscle mass, lifestyle habits, and more. Additionally, having high levels of creatinine doesn’t necessarily mean you have kidney disease. For instance, your creatinine levels could be influenced by:

• Supplementing with creatine
• Having an extremely muscular body
• Eating a high-protein diet that includes a lot of meat
• Engaging in a high-intensity workout before the test
• Taking certain medications like cimetidine, cobicistat, ritonavir, or dolutegravir
• Using medications like fenofibrate (for high triglycerides) or trimethoprim (for urinary tract infections)
• Dehydration

People can also experience low levels of creatinine. Sometimes low readings can be linked to an issue like malnutrition, age-related muscle loss, or even liver disease (or cirrhosis). Here are some other potential explanations for low creatinine levels:

• Being pregnant
• Having a limb amputated
• Experiencing sarcopenia (or a type of muscle-wasting disease)
• Following a low-protein diet or being vegan or vegetarian
• Being diagnosed with a neuromuscular disorder like muscular dystrophy
• Having very little muscle on your body

How Is Creatinine Measured?

Usually, your creatinine levels are checked as part of your normal blood work, unless a provider is looking for chronic kidney disease (or renal disease) or wants to see how certain medications are affecting your kidneys. They may also order kidney tests if you’ve recently had a kidney transplant or you have a condition like diabetes or high blood pressure.

Creatinine levels are often measured using a blood test that looks for the level of serum creatinine in your blood. This measurement is listed on your lab results in milligrams of creatinine per deciliter of blood. It may also be listed as micromoles per liter of blood. The normal range of creatinine for adult women is from 0.59 to 1.04 milligrams per deciliter, and for adult men it’s from 0.74 to 1.35 milligrams per deciliter.

Sometimes a healthcare provider will use both blood work and urinalysis (or a urine test) to determine your creatinine levels. Here are some of the tests used to check creatinine levels.

Estimated Glomerular Filtration Rate

The estimated glomerular filtration rate (eGFR) uses the levels of creatinine in your blood, along with your age and sex, to determine how fast creatinine is filtered out of your body. It also helps show your kidney health and provides information about the seriousness of kidney disease. Your eGFR score can be calculated using either your cystatin C level or your serum creatinine level, or it can be calculated using both measurements. When both levels are used, the results tend to be more accurate.

Creatinine Clearance

Similar to the eGFR test, the creatinine clearance test is used to determine how fast your kidneys filter out creatinine. This test can be helpful for assessing amputees and people with very high or very low muscle mass, but it can be less accurate if the urine collection is incomplete.

Urine Albumin to Creatinine Ratio

With the urine albumin to creatinine ratio (UACR) test, healthcare providers are looking at the ratio of albumin to creatinine in your urine. This ratio is measured using the number of milligrams of albumin for every gram of creatinine. In adult women, healthy kidneys would have less than 25 milligrams per gram, while adult men would have less than 17 milligrams per gram, according to Mayo Clinic. Results outside the typical range may mean that you have developed nephropathy (a type of kidney damage).

Blood Urea Nitrogen-to-Creatinine Ratio

The blood urea nitrogen-to-creatinine ratio test measures the amount of urea, a waste product, in your blood compared to the amount of creatinine. Your blood urea nitrogen (BUN) combined with your creatinine level can be used to find the BUN to creatinine ratio. Higher BUN levels may mean you’re dehydrated, but they also can be a sign of heart disease.

Urine Creatinine

The urine creatinine test involves giving a urine sample either one time or over the course of 24 hours to measure the level of creatinine in your urine. Your results are measured in either grams or millimoles per day. For adult women, the normal range is 0.6 to 1.6 grams per day, and for adult men it’s 0.8 to 1.8 grams per day.

Why Measuring Creatinine Is Important

If there’s no reason to suspect kidney disease, your creatinine levels will likely be measured during a routine physical when your healthcare provider orders a complete metabolic panel. Tracking your creatinine levels regularly allows your provider to identify any sudden changes that could indicate an underlying issue like impaired kidney function.

Measuring your creatinine can also be useful if you have signs of kidney disease but have not been diagnosed. Some indicators that you may need more testing include having dry or itchy skin, changes in urination, shortness of breath, foamy urine, puffy eyelids, and swelling. Talk to your healthcare provider about these symptoms, and ask if you may need a creatinine test.

Finding kidney disease early can significantly slow its progression and protect your kidney health. In fact, researchers have found that when kidney disease is discovered early, treatment plans can reduce the risk of complications and decrease death rates.

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