Seeing “high creatinine” on a blood test can be alarming, especially when you know creatinine is often used to assess kidney function. But sometimes, the number can rise for reasons that have little to do with kidney disease.

Creatinine is a waste product your muscles make, and your kidneys filter it out of your blood. It’s easy to confuse it with creatine, the supplement some people take for muscle strength and exercise performance, but they’re not the same.

Here’s what a high creatinine level can mean, what causes it, how healthcare providers evaluate it, and when it’s time to reach out to your care team.

What Causes High Creatinine Levels?

A high creatinine level doesn’t always mean you have kidney disease. It can also have a temporary cause or occur for reasons unrelated to kidney function. Common causes include:

Some of these causes point to a problem with the kidneys themselves, while others are unrelated to kidney health.

Kidney-Related Causes

Kidney disease, kidney injury, a kidney infection, or a urinary blockage can raise creatinine levels. Dehydration, heart failure, and diabetes can also cause creatinine to rise. Your provider may order more tests to find out what’s causing the change.

Nonkidney Causes

Creatine supplements, high muscle mass, or eating large amounts of cooked meat can also raise your levels — as can a recent high-intensity workout or certain medications, including cimetidine (Tagamet), cobicistat (Tybost), ritonavir (Norvir), dolutegravir (Tivicay), fenofibrate (TriCor), and trimethoprim.

Creatinine levels can also run low from malnutrition or reduced muscle mass.

How Is High Creatinine Evaluated?

If your creatinine is high, your healthcare provider may first repeat the test to confirm the result. They may also check your eGFR or order other tests, such as a urine albumin-to-creatinine ratio (UACR) or blood urea nitrogen (BUN) test. These tests can help your doctor understand what may be causing the change.

Each test measures something different, and no single one tells the whole story.

Serum Creatinine and Urinalysis

Repeating your serum creatinine test is often the first step because levels can fluctuate for reasons unrelated to your kidneys. It may be measured alone or as part of a comprehensive metabolic panel. Your provider may also order a urinalysis, a general urine test, to check for other signs of kidney problems, such as protein or blood in your urine.

Estimated Glomerular Filtration Rate

The estimated glomerular filtration rate (eGFR) can use your creatinine level, along with your age and sex, to estimate how well your kidneys filter waste. It also helps show how severe kidney disease is, if you have it.

Your eGFR can be calculated using your creatinine level, your cystatin C level, or both. Using both tends to be more accurate than either alone. Reference ranges for creatinine can vary by lab.

Your healthcare provider will interpret your creatinine and eGFR results based on factors such as your age, sex, muscle mass, diet, and activity level.

Creatinine Clearance

Creatinine clearance estimates how well your kidneys filter creatinine using both a blood test and a timed urine sample. It may be useful in certain situations when an additional measure of kidney function is needed, such as in people with very high or low muscle mass or in people who have had an amputation.

Urine Albumin-to-Creatinine Ratio

The urine albumin-to-creatinine ratio compares the amount of albumin (a protein) to creatinine in your urine.

A lower UACR is generally better, with less than 30 milligrams per gram considered normal for adults. A result of 30 milligrams per gram or higher usually needs to be confirmed with repeat testing before it’s considered a sign of kidney damage.

Blood Urea Nitrogen-to-Creatinine Ratio

The blood urea nitrogen (BUN)-to-creatinine ratio compares BUN with creatinine. Both are waste products that your kidneys filter from your blood. A high ratio can mean you’re dehydrated, but it can also happen with conditions like heart failure, gastrointestinal bleeding, or a high-protein diet, and some medicines can raise it too.

On its own, a BUN result isn’t enough to diagnose a kidney condition. Instead, it helps your provider interpret the bigger picture alongside your other results.

Urine Creatinine

A urine creatinine test measures creatinine in your urine using either a single sample or a 24-hour urine collection. Results may be reported in different units depending on the type of urine sample, and what counts as normal depends on the reference range your specific lab uses.

In some cases, your provider may also recommend imaging, such as a kidney ultrasound, or other lab work to look more closely at what’s causing your results.

What Happens Next?

A high creatinine level is a starting point for a conversation with your healthcare provider, not a diagnosis on its own.

A few questions worth bringing to your next appointment:

Tell your provider if you notice changes in urination, swelling in your legs, ankles, or around your eyes, foamy urine, ongoing fatigue, or shortness of breath. These can be signs of kidney disease and should be discussed with your healthcare provider.

Catching changes in kidney function early gives you and your provider more options for managing it. If you haven’t had a creatinine test recently, or if something about your result doesn’t add up, reach out to your provider and ask what your numbers mean for you.