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).
As people age, their creatinine level usually decreases because of the natural loss of muscle mass and lack of physical activity that could maintain it. Also, when the body doesn’t receive enough calories from food, it adjusts to the new nutritional limitations by decreasing the metabolism and starts breaking down fat and protein for fuel, resulting in muscle loss. But if the malnutrition continues, the body will be no longer able to maintain an optimal level of functioning.
A good example of the relation between nutrition and the creatinine levels is the vegetarian diet. The creatinine levels of vegetarians are usually lower than those of people who eat meat, since animal protein contributes to the blood creatinine level.
Finally, pregnancy can also cause the creatinine levels to go down because during pregnancy, the kidneys are more efficient at clearing creatinine and other waster products from the blood. And a rather uncommon reason for low blood creatinine can be prolonged excess water consumption.
Is there a reason for concern?
Sometimes, the reason behind low blood creatinine levels can be advanced liver disease. Since the liver is most responsible for creating protein and breaking protein down in the body, when it’s not functioning properly, it’s efficiency at managing protein is damaged and creatinine levels in the blood go down. This is why the creatinine clearance test is crucial for determining of how well the kidneys are working.
It’s important to note that certain medications can interfere with the results, so it’s best to consult with your doctor and inform him about all the factors that could potentially cause the creatinine levels to be lower or higher than normal – including the diet, previous or ongoing medical conditions, currently used medications and pregnancy – so that he can decide if further tests and analysis are needed.