Do gym exercises increase blood creatinine levels and what is the underlying mechanism?

From the Guidelines

Yes, gym exercises, especially intense resistance training, can temporarily increase blood creatinine levels. This occurs because physical exertion causes increased muscle breakdown and turnover, releasing creatinine (a waste product of creatine phosphate metabolism in muscles) into the bloodstream. The mechanism involves both acute and chronic effects: during intense exercise, rapid energy utilization in muscles breaks down creatine phosphate, producing creatinine; additionally, exercise-induced muscle damage releases more creatinine into circulation. Muscle mass also plays a role, as individuals with greater muscle mass typically have higher baseline creatinine levels. This elevation is usually transient, with levels returning to baseline within 24-48 hours after exercise. For accurate kidney function assessment, blood tests should be conducted after at least 24 hours of rest from strenuous exercise, as exercise within 24 h can elevate urinary albumin-to-creatinine ratio (UACR) independently of kidney damage 1. While this increase is generally normal and not concerning, consistently elevated creatinine levels unrelated to exercise timing should prompt medical evaluation to rule out kidney issues.

Key Points to Consider

• The increase in blood creatinine levels after gym exercises is usually temporary and returns to baseline within 24-48 hours.
• Muscle mass plays a role in baseline creatinine levels, with individuals having greater muscle mass typically having higher levels.
• Exercise-induced muscle damage can release more creatinine into circulation, contributing to the increase in blood creatinine levels.
• For accurate kidney function assessment, blood tests should be conducted after at least 24 hours of rest from strenuous exercise.
• Consistently elevated creatinine levels unrelated to exercise timing should prompt medical evaluation to rule out kidney issues, as recommended by the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation 1.

Mechanism of Action

The mechanism of action involves the breakdown of creatine phosphate in muscles during intense exercise, producing creatinine, which is then released into the bloodstream. Additionally, exercise-induced muscle damage can release more creatinine into circulation, contributing to the increase in blood creatinine levels. The lymphatic clearance of creatinine from the extracellular space can lead to difficulties in interpreting enzyme activity in blood, as the transport from the damaged tissue to the venous angle of the left subclavian and internal jugular veins takes time, resulting in a delay between the release from the muscles and measurability in the blood 1.

Clinical Implications

The clinical implications of this increase in blood creatinine levels are important to consider. While the increase is generally normal and not concerning, consistently elevated creatinine levels unrelated to exercise timing should prompt medical evaluation to rule out kidney issues. The American Diabetes Association recommends promptly referring to a nephrologist for uncertainty about the etiology of kidney disease, difficult management issues, and rapidly progressing kidney disease 1. Additionally, the use of blood-based biomarkers, such as creatine kinase, can be useful in monitoring muscle damage and guiding exercise, but their interpretation should be done with caution, considering alternative explanations for biomarker increases and/or differences between athletes 1.

From the Research

Gym Exercises and Blood Creatinine Levels

• Gym exercises can increase blood creatinine levels, but the underlying mechanism is not directly related to kidney damage 2.
• Exercise-induced muscle damage can lead to increased serum creatine kinase (CK) levels, which can be misinterpreted as kidney dysfunction 2.
• Creatinine is a byproduct of creatine metabolism, and increased creatine supplementation can elevate serum creatinine levels without affecting kidney function 3.

Effects of Exercise on Creatinine Levels

• Low-intensity exercises have been shown to decrease serum creatinine levels in patients with chronic kidney disease 4.
• High-intensity exercises, on the other hand, can increase serum CK levels, which may be correlated with physical training status and muscle damage 5, 2.
• The relationship between exercise intensity and creatinine levels is complex and requires further investigation.

Mechanism of Creatinine Elevation

• Creatine supplementation can increase serum creatinine levels by increasing the amount of creatine available for metabolism 6, 3.
• Exercise-induced muscle damage can lead to the release of CK into the bloodstream, which can be misinterpreted as kidney dysfunction 2.
• The kidneys play a role in filtering creatinine from the blood, but exercise-induced changes in blood flow and muscle metabolism can affect creatinine levels independently of kidney function 4, 2.