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 age, race, gender, body size, activity level and medications.
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 recomme
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 can be tested in both the blood and in the urine. These tests can help evaluate 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, gender and race, 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 Purivo 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.
Are there any instances when creatinine alone can be used to determine kidney function?
This is an important question. There is a difference between looking at creatinine in your bloodstream (called “serum creatinine”) and looking at creatinine in your urine (called “creatinine clearance”). These are two different lab tests. Serum creatinine is part of a routine lab report; creatinine clearance is not.
Creatinine clearance requires a timed urine sample. All the urine you have passed within a specific time period – usually 24-hours – is saved (collected) in a container and tested. The result shows how much creatinine has passed through your kidneys into your urine. It helps show how well your kidneys are removing the waste products from your blood.
Can my healthcare provider know if my kidneys are working properly by looking at how much creatinine is in my blood?
No. Looking at how much creatinine is in your blood is not the best way to check your kidney health. That’s because the level of creatinine in your blood is affected by your age, race, gender, and body size. (In other words, what’s considered “normal” depends on these factors.) The best way to know if your kidneys are working properly is by looking at your glomerular filtration rate (GFR).
GFR is a routine lab that can be found on your blood work report. GFR is a calculation that includes your creatinine, along with your age, gender, race, and weight. Your GFR number will help your healthcare provider know if you have kidney disease. You may have kidney disease if your GFR number is:
- Below 60 for three months
- Above 60 with signs of kidney damage (having protein in the urine is a sign of kidney damage)
Do I need any other tests?
Yes, another important test to check kidney function is a urine test. You will be asked to pee into a clean cup called a specimen cup. Only about two tablespoons of urine is needed to do the test. The urine will be sent to a laboratory, where a test called an ACR (albumin-to-creatinine ratio) is done. An ACR shows whether you have a type of protein called albumin in your urine. A normal amount of albumin in your urine is less than 30 mg/g. Anything above 30 mg/g may mean you have kidney disease, even if your GFR number is above 60.
This test is also used to look at how likely it is that a person’s kidney disease will get worse. This is called risk for progression. Having high amounts of albumin points to a higher risk.