Creatine and Kidneys: Why Can Creatinine Levels Rise?

Creatine is one of the most studied dietary supplements in sports nutrition. However, a question often arises among those who use it: can creatine increase creatinine levels, and should one worry about kidney health?

This question primarily stems from a confusion between two molecules with similar names: creatine and creatinine.

Creatine is a compound naturally present in the body and involved in the energy function of muscles. Creatinine, on the other hand, is a product primarily derived from the metabolism of creatine and muscle phosphocreatine.

Creatinine is used as one of the markers to assess kidney function. An increase in its concentration in the blood can therefore raise concern during an analysis.

But higher creatinine levels do not automatically mean less healthy kidneys.

To understand why, it is necessary to distinguish between creatine supplementation, creatinine production, and the various parameters used to assess kidney function.

Creatine and Creatinine: What's the Difference?

Before discussing kidneys, it is essential not to confuse these two molecules.

Creatine

Creatine is naturally present in the body, primarily in muscles.

It participates in the energy system, particularly allowing for rapid ATP regeneration during short, intense efforts.

Part of the creatine present in muscles is also stored as phosphocreatine.

Creatine monohydrate supplementation increases muscle reserves of creatine and phosphocreatine.

Creatinine

Creatinine is a product derived from the metabolism of creatine and phosphocreatine.

It is produced relatively consistently, especially depending on muscle mass, and then primarily eliminated by the kidneys.

It is precisely this renal elimination that explains why blood creatinine is used in the evaluation of kidney function.

Creatine and creatinine are therefore related, but they are two different molecules that should not be confused.

 

What is Creatinine?

Creatinine is a metabolic waste product generated primarily from creatine and phosphocreatine present in muscles.

It then enters the bloodstream before being mainly eliminated by the kidneys.

When kidney function declines, creatinine elimination can be less efficient, and its blood concentration may increase.

This is why creatinine is one of the parameters commonly measured during a biological assessment.

But there is an important limitation: creatinine concentration also depends on factors not directly related to kidney function.

Muscle mass, physical activity, diet, and certain supplements can notably influence its concentration.

 

Why can Creatine Increase Creatinine?

Taking creatine can lead to a change in the measured blood creatinine concentration in some individuals.

This is partly explained by the fact that some of the creatine in the body is converted into creatinine.

Supplementation increases the available creatine reserves in the muscles. It can therefore also alter the amount of creatinine produced.

Thus, an increase in creatinine in someone taking creatine does not, by itself, allow for the conclusion of a deterioration in kidney function.

This is one of the reasons why interpreting an analysis must take context into account.

The pitfall of an isolated marker

A biological result should not be interpreted independently of the person from whom it was measured.

The same creatinine value can have a different meaning depending on:

• muscle mass;
• age;
• sex;
• level of physical activity;
• diet;
• creatine intake;
• hydration;
• other biological results.

This is why doctors generally do not rely solely on the raw creatinine concentration to assess kidney function.

 

Does high creatinine necessarily mean a kidney problem?

No.

High blood creatinine can be associated with decreased renal filtration, but it can also be influenced by other factors.

For example, in a very muscular person, creatinine production may be higher than in a person with less muscle mass.

Intense exercise can also temporarily alter certain biological parameters.

Creatine consumption is another factor to consider.

It would therefore be incorrect to consider that high creatinine automatically equates to kidney failure.

The pertinent question is rather: why is creatinine elevated, and what do other indicators of kidney function show?

 

Why can athletes have higher creatinine?

Athletes are a particularly interesting case when interpreting creatinine.

Since creatinine is notably derived from muscle metabolism, its production is influenced by the amount of muscle present in the body.

A person who regularly practices weight training and has significant muscle mass may therefore exhibit a different creatinine concentration than a less muscular person.

This difference does not necessarily mean that kidney function is different.

Training can also modify results

Intense training can lead to various transient changes in certain blood parameters.

After a particularly demanding session, some markers may thus differ from those observed at rest.

For this reason, the context in which a blood analysis is performed can be important.

A blood test performed on an athlete must be interpreted taking into account their level of physical activity and muscle mass.

 

What factors can vary creatinine?

Creatinine does not depend exclusively on the kidneys.

Several factors can influence its blood concentration.

Muscle mass

The greater the muscle mass, the higher the creatinine production can be.

This is why the values observed in a very muscular athlete should not necessarily be compared directly to those of a person with much lower muscle mass.

Physical activity

Intense exercise can temporarily influence various biological markers.

The date and intensity of the last training session can therefore provide useful information when interpreting a balance sheet.

Diet

Certain dietary factors can also alter creatinine concentration.

For example, high meat consumption can temporarily influence measured creatinine in certain circumstances.

Creatine supplementation

Creatine consumption is obviously important information to communicate when a blood analysis is interpreted.

It can alter creatinine concentration without necessarily indicating an impairment of kidney function.

Hydration

The level of hydration can also influence certain measured concentrations in the blood.

Significant dehydration can notably alter certain biological parameters and complicate their interpretation.

 

Creatinine and GFR: What's the difference?

Creatinine is often used to estimate the glomerular filtration rate (GFR), also called eGFR when estimated from a formula.

GFR provides an estimate of the kidneys' ability to filter blood.

Unlike a simple creatinine concentration, the GFR estimate takes into account several characteristics of the person and allows for a more informative interpretation of kidney function.

But here again, formulas based on creatinine have certain limitations.

In individuals with particularly high or low muscle mass, for example, the relationship between creatinine and renal filtration can be less straightforward.

Therefore, the GFR estimated from creatinine must also be interpreted within its clinical context.

 

Why might Cystatin C be useful?

Cystatin C is another marker used to assess kidney function.

Its advantage is notably that it is less directly influenced by muscle mass than creatinine.

In certain situations where creatinine interpretation is difficult, especially in individuals with atypical body composition, cystatin C can therefore provide complementary information.

Recommendations and scientific work particularly consider the use of cystatin C, alone or combined with creatinine, as an approach to improve the estimation of kidney function in certain situations.

For an athlete taking creatine and presenting elevated creatinine, a healthcare professional may therefore decide that another marker or a complementary examination is relevant.

 

How to interpret a blood test when taking creatine?

If you are taking creatine and your creatinine level is above a reference value, it is important not to draw conclusions based solely on this result.

Several factors must be taken into account:

• the dose of creatine consumed;
• the duration of supplementation;
• muscle mass;
• the level of physical activity;
• the date of the last training session;
• hydration;
• other parameters of the blood test;
• any medical history.

The doctor can then determine whether the observed value corresponds to an expected variation or if it warrants further investigation.

A single analysis does not always tell the whole story

When a result is unusual, its evolution over time can be informative.

Comparing several blood tests performed under similar conditions can help to better understand a variation.

However, one should not attempt to interpret a biological value alone outside of its medical context.

To learn more about interpreting blood tests and understanding what a high creatine or creatinine level might mean, also consult our article Creatine in the blood: what does a high level mean?.

 

Should you stop creatine before a blood test?

There is no universal rule requiring creatine to be stopped before any blood test.

The course of action primarily depends on the reason for the test and the parameters being sought.

If the objective is notably to evaluate kidney function, it is important to inform the healthcare professional that you are taking creatine.

This information allows for proper interpretation of results and, if necessary, the selection of complementary markers.

It is therefore not recommended to unilaterally change a treatment or supplementation in order to "make disappear" a high value on an analysis.

The most important thing is that the professional interpreting the blood test is aware of the supplementation being used.

 

Is creatine bad for the kidneys?

The question of creatine's renal safety has been the subject of much research.

In healthy adults, available data do not show that usual doses of creatine monohydrate lead to kidney function deterioration.

Controlled studies and literature reviews have notably evaluated various markers of kidney function in individuals consuming creatine.

However, it is essential to distinguish between two questions:

• can creatine alter measured creatinine? Yes, this can happen;
• does an increase in creatinine automatically mean that creatine has damaged the kidneys? No.

This distinction is precisely what explains some of the concerns surrounding creatine and the kidneys.

For a detailed analysis of creatine safety and available data, also consult our article Creatine for bodybuilding: a danger?.

 

When to seek medical advice?

High creatinine should not be interpreted alone, especially when associated with other biological abnormalities or symptoms.

Medical advice is particularly important when an abnormality persists, when it is significant, or when it is accompanied by other abnormal results.

The healthcare professional can notably determine whether it is necessary to:

• repeat the analysis;
• examine the estimated GFR;
• measure cystatin C;
• analyze urine;
• consider other biological parameters;
• look for another possible cause of the elevated creatinine.

A blood test must always be interpreted within its medical context.

 

Creatine, creatinine, and kidneys: why does this confusion persist?

The confusion largely stems from the similarity of the two terms.

Creatine is a compound naturally present in muscles and widely used as a dietary supplement.

Creatinine is a product of its metabolism that circulates in the blood, and its elimination notably depends on the kidneys.

Since creatinine is used to assess kidney function, any variation can naturally cause concern.

However, a variation in this marker is not, by itself, synonymous with kidney damage.

This is why the athlete's context and creatine consumption must be known when interpreting the blood test.

 

Key Takeaways

• Creatine and creatinine are two different molecules.
• Creatinine is produced primarily from the metabolism of muscle creatine and phosphocreatine.
• Blood creatinine is used as one of the markers to assess kidney function.
• Taking creatine can lead to an increase in measured creatinine in some individuals.
• Elevated creatinine does not automatically mean that the kidneys are damaged.
• Muscle mass, exercise, diet, hydration, and certain supplements can influence creatinine levels.
• The estimated GFR provides complementary information to a simple creatinine concentration.
• Cystatin C can be useful in certain situations where creatinine interpretation is more complex.
• It is important to inform your healthcare professional about your creatine consumption when interpreting a blood test.
• In healthy adults, available data do not show deterioration of kidney function related to usual doses of creatine monohydrate.
• In case of an abnormal or persistent result, only a healthcare professional can determine what it means in your specific situation.
  

Creatine and creatinine are not synonymous. Creatine supplementation can alter measured blood creatinine levels, but this variation alone does not allow for a conclusion of impaired renal function. In athletes, muscle mass, training, and supplementation must be considered to correctly interpret test results.

 

Scientific Sources

• Kreider RB, Kalman DS, Antonio J, et al. International Society of Sports Nutrition position stand: safety and efficacy of creatine supplementation in exercise, sport, and medicine. Journal of the International Society of Sports Nutrition. 2017.
• Antonio J, Candow DG, Forbes SC, et al. Common questions and misconceptions about creatine supplementation: what does the scientific evidence really show? Journal of the International Society of Sports Nutrition. 2021.
• Kreider RB, Stout JR. Creatine in Health and Disease. Nutrients. 2021.
• Wyss M, Schulze A. Health implications of creatine: can oral creatine supplementation protect against neurological and atherosclerotic disease? Physiological Reviews. 2002.
• Inker LA, Eneanya ND, Coresh J, et al. New Creatinine- and Cystatin C–Based Equations to Estimate GFR without Race. New England Journal of Medicine. 2021.
• KDIGO. 2024 Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease. Kidney International. 2024.