Creatinine

Creatinine is a waste product that is produced continuously during normal muscle breakdown. The kidneys filter creatinine from the blood into the urine, and reabsorb almost none of it.

Overview

Creatinine is a chemical waste molecule that is generated from muscle metabolism. The molecule is produced from creatine, a molecule of major importance for energy production in muscles. Approximately 2% of the body's creatine is converted to creatinine every day. Creatinine is transported through the bloodstream to the kidneys. The kidneys filter out most of the creatinine and dispose of it in the urine.

Measurement of Creatinine

The creatinine blood test is used to assess kidney function. It is frequently ordered along with a BUN (blood urea nitrogen) test, or as part of a comprehensive metabolic panel (CMP) or a basic metabolic panel (BMP) to evaluate the status of a person's kidneys.

Creatinine Clearance Test

A creatinine clearance test measures creatinine levels in both a sample of blood and a sample of urine from a 24-hour urine collection. The results are used to calculate the amount of creatinine that has been cleared from the blood and passed into the urine. This calculation allows for a general evaluation of the amount of waste products that are being removed by the kidneys and an overall efficiency of the filtration process.

High and Low Creatinine Levels

High levels of creatinine in the blood and/or decreased creatinine clearance may indicate that the kidneys are not working properly. Low levels of creatinine in the blood may be seen with conditions that result in decreased muscle mass.

See Also

• Kidney function
• Kidney disease
• Chronic kidney disease
• Acute kidney injury
• Glomerular filtration rate

References

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  Creatinine tautomerism 2D skeletal
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  Blood values sorted by mass and molar concentration