From the Guidelines
Creatine and creatinine are distinct compounds with different roles in the body, and while creatine supplementation may slightly increase creatinine levels, it does not typically reflect kidney damage in healthy individuals. The key difference between creatine and creatinine lies in their functions and how they are utilized or produced by the body. Creatine is a substance that helps produce energy during high-intensity exercise and can be taken as a dietary supplement to enhance athletic performance, typically at a loading dose of 20 grams daily (divided into 4 doses) for 5-7 days, followed by a maintenance dose of 3-5 grams daily 1. On the other hand, creatinine is a waste product formed from the breakdown of creatine in muscles, filtered from the blood by the kidneys, and excreted in urine. Creatinine levels in blood are used as a biomarker to assess kidney function, with elevated levels potentially indicating kidney problems 1. It's crucial to understand that serum creatinine concentration is affected by factors other than glomerular filtration rate (GFR), such as creatinine secretion and generation and extrarenal excretion, making it challenging to use serum creatinine concentration alone to estimate the level of kidney function or to detect earlier stages of chronic kidney disease 1. Clinicians should not use serum creatinine concentration as the sole means to assess the level of kidney function, and clinical laboratories should report an estimate of GFR using a prediction equation in addition to reporting the serum creatinine measurement 1. People with pre-existing kidney conditions should consult healthcare providers before taking creatine supplements, as the relationship between creatine and creatinine explains why athletes using creatine supplements might show slightly higher creatinine levels on blood tests without having kidney issues. Some key points to consider include:
- Creatine supplementation does not typically cause kidney damage in healthy individuals but may slightly increase creatinine levels.
- Creatinine levels are used to assess kidney function, with elevated levels potentially indicating kidney problems.
- Serum creatinine concentration alone is not a reliable indicator of kidney function due to various influencing factors.
- GFR estimation using prediction equations is recommended for a more accurate assessment of kidney function.
From the Research
Creatine vs Creatinine: Understanding the Difference
- Creatine and creatinine are two distinct substances that are often confused with each other due to their similar names.
- Creatine is a substance that is naturally produced by the body and is also available as a dietary supplement, often used to improve athletic performance 2.
- Creatinine, on the other hand, is a waste product that is produced by the body as a result of muscle metabolism and is typically measured to assess kidney function 3, 4, 5, 6.
Creatinine as a Marker of Kidney Function
- Serum creatinine levels are widely used as a marker of kidney function, as they are simple, fast, and inexpensive to measure 3, 4, 5.
- However, creatinine levels can be influenced by various factors such as age, physical activity, diet, and ethnicity, which can limit its accuracy as a marker of kidney function 3, 4, 5.
- Alternative markers such as cystatin C have been proposed as potentially more accurate measures of kidney function, but their use is not yet widely established 2, 3, 5.
Clinical Applications of Creatinine Measurement
- Creatinine measurement is commonly used to assess kidney function in patients with chronic kidney disease, as well as to monitor the effectiveness of treatments such as dialysis 4, 5.
- Point-of-care creatinine tests have been developed to allow for rapid measurement of kidney function in outpatient settings, such as before contrast-enhanced CT imaging 6.
- These tests have been shown to be effective in identifying patients at risk of kidney injury, but their cost-effectiveness and clinical outcomes are still being evaluated 6.