What is the Difference Between Creatinine and Creatine Kinase

The main difference between creatinine and creatine kinase is that creatinine is a breakdown product of creatine phosphate from muscle and protein metabolism whereas creatine kinase is the enzyme that converts creatine into creatine phosphate.

In general, creatinine and creatine kinase are two related objects to creatine, which is an organic compound that facilitates ATP recycling in muscle and brain tissue.

Key Areas Covered

1. What is Creatinine
   • Definition, Characteristics, Importance
2. What is Creatine Kinase
   • Definition, Characteristics, Importance
3. Similarities Between Creatinine and Creatine Kinase
   • Outline of Common Features
4. Difference Between Creatinine and Creatine Kinase
   • Comparison of Key Differences

Key Terms

Creatine Kinase, Creatinine

What is Creatinine

Creatinine is a biological waste product formed by the degradation of creatine in muscle cells. The blood transport creatinine from muscles to the kidney where the creatinine undergoes excretion. The amount of creatinine in blood is proportional to the muscle mass in the body in a healthy person. Moreover, blood creatinine levels reflect the level of kidney function. Generally, the blood creatinine level of a man with normal kidney function is around 0.6 to 1.2 mg/mL. Since women have a low muscle mass compared to men, their blood creatinine levels are lower than that of men.

Figure 1: Creatinine

Furthermore, blood creatinine level also depends on the activity of the body and medications. More importantly, serum creatinine level is tested for the determination of glomerular filtration rate (GFR). The low GFR elevates the blood creatinine level. In general, the detection of high creatinine levels in ordinary blood is a symptom of weak kidney function. Moreover, blood creatinine level is increased in chronic kidney disease and it is one of the factors used in recommending dialysis for a patient. In addition, the creatinine clearance test measures the clearing out of creatinine from the blood. It is done by measuring creatinine levels in blood and urine.

What is Creatine Kinase

Creatine kinase is the enzyme responsible for ATP recycling in the tissues that consume ATP rapidly. Examples of such tissues are the skeletal muscles, smooth muscles, brain, photoreceptor cells of the retina, hair cells of the inner ear, and spermatozoa. The main function of creatine kinase is to convert creatine into creatine phosphate while converting ATP to ADP. In general, this creatine phosphate serves as an energy reservoir for the rapid regeneration of ATP. Normally, this creatine phosphate converts into creatinine proportional to the muscle mass, and creatinine excretes through urine.

Figure 2: Creatine Kinase

Moreover, creatine kinase primarily occurs in the cytosol and it has four isoenzymes with the variable distribution. Generally, they are CK-1 predominates in the brain; CK-2 and CK-3 in cardiac and skeletal muscle, and CK-Mt in mitochondria of various tissues.

Similarities Between Creatinine and Creatine Kinase

• In general, creatinine and creatine kinase are two substances related to creatine.
• They are also important in the ATP recycling in muscles and the brain.

Difference Between Creatinine and Creatine Kinase

Definition

Creatinine refers to a compound produced by the metabolism of creatine and excreted through urine. Meanwhile, creatine kinase refers to any of the three isoenzymes found especially in vertebrate skeletal and myocardial muscle that catalyze the transfer of a high-energy phosphate group from phosphocreatine to ADP with the formation of ATP and creatine.

Significance

Generally, creatinine is a breakdown product of creatine phosphate from muscle and protein metabolism while creatine kinase is the enzyme that converts creatine into creatine phosphate.

Importance

Moreover, creatinine is released at a constant rate by the body depending on the muscle mass while creatine kinase recycles ATP in tissues with rapid ATP consumption.

Conclusion

In brief, creatinine and creatine kinase are two related substances in tissues with high ATP consumption. Some examples of such tissues include the skeletal muscle and the brain. Creatinine is a metabolic byproduct of the creatine in muscles and it is continuously removed from the body through urine. Whereas, creatine kinase is an enzyme that converts creatine into creatine phosphate, recycling ATP. Therefore, the main difference between creatinine and creatine phosphate is their function.

References:

1. Wikimedia Foundation. (2022, August 30). Creatinine. Wikipedia. Retrieved September 28, 2022.
2. Creatine kinase. Creatine Kinase – an overview | ScienceDirect Topics. (n.d.). Retrieved September 28, 2022.

Image Courtesy:

1. “Creatinine” By Jesse – Own work (CC BY-SA 3.0) via Commons Wikimedia
2. “Creatine-Kinase” By Hbf878 – Own Work (CC0) via Commons Wikimedia