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What Is Creatinine?

Creatinine is a chemical waste product in the blood that passes through the kidneys to be filtered and eliminated in urine. The chemical waste is a by-product of normal muscle function. The more muscle a person has, the more creatinine they produce. Levels of creatinine in the blood reflect both the amount of muscle a person has and their amount of kidney function.

Most men with normal kidney function have approximately 0.6 to 1.2 milligrams/deciliters (mg/dL) of creatinine. Most women with normal kidney function have between 0.5 to 1.1 mg/dL of creatinine. Women usually have lower creatinine levels than men because women, on average, have less muscle than men.

Other factors that may affect the level of creatinine in the blood include body size, activity level and medications.

Creatinine and chronic kidney disease

When there is kidney damage or kidney disease, and the kidneys are not able to filter waste efficiently, there will likely be a rise in creatinine levels in the blood. Dialysis is needed whenever kidney function is too low to maintain health. However, creatinine is just one of many factors considered when deciding whether or not to recommend dialysis treatment.

Symptoms of too little kidney function

Some people who have no symptoms of illness at all find out they have advance kidney disease when high creatinine levels are detected in routine blood tests. When signs of too little kidney function do arise, they may include loss of appetite, vomiting, itching, weakness and flu-like symptoms.

Swelling in the legs and shortness of breath may occur if water builds up in the body.

Creatinine tests 

Creatinine can be tested in both the blood and in the urine. These tests can help evaluate change in kidney function.

Serum creatinine is a test that draws blood and sends it to a laboratory to be analyzed to find out how much creatinine is in the bloodstream.

Knowing your serum creatinine allows your doctor to calculate your creatinine level along with your age and gender to determine your glomerular filtration rate (GFR). GFR is a measure of kidney function. If you know a serum creatinine level, you can determine the stage of CKD using the DaVita GFR Calculator. A low GFR, just like an elevated serum creatinine, is not always evidence of kidney disease. Ask your doctor to help you interpret your results.

Creatinine clearance (Ccr or CrCl) measures how much creatinine is cleared out of the body, or how well kidneys filter waste. Creatinine clearance requires a combination of a urine test and blood test. Because the urine has to be collected over a period of 24 hours, the creatinine clearance is usually done after first evaluating the serum creatinine and calculating the GFR.