Creatinine is a waste product created from the normal breakdown of muscle tissue, and the kidneys are responsible for filtering it from the blood into the urine. In fact, doctors test the kidney function by measuring the blood creatinine level. The amount of blood the kidneys can make creatinine-free in one minute is called the creatinine clearance – around 125 milliliters per minute in a healthy young adult.
The creatinine clearance is further used to estimate the glomerular filtration rate (GFR), or the rate of blood flow through the kidneys, which can vary depending on age, sex and size. That means that testing the rate of creatinine clearance shows the kidney’s ability to filter the blood. If the kidneys are damaged and can’t work optimally, the amount of creatinine in the urine goes down, while its level in the blood goes up.
What’s the reason for low blood levels of creatinine?
High blood levels of creatinine almost always suggest a kidney disease, most often including damaged blood vessels, infections or death of cells caused by toxins.
Low blood levels of creatinine are not common, but usually don’t suggest serious issues and can be often observed in medical conditions associated with decreased muscle mass. In fact, low muscle mass is the leading cause of a low level of creatinine, and the most common reasons for muscle loss are certain diseases that lead to severe muscle atrophy, aging and malnutrition (especially diets that are very low in protein).
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