What Is Creatinine?

People who have chronic kidney disease (CKD) may have heard their nephrologist or nurse talk about creatinine. So what is creatinine exactly? 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 contractions. Creatinine is made from creatine, a supplier of energy to the muscle.

Women usually have lower creatinine levels compared to men, because women have less muscle tissue. Among adults without kidney disease, men have approximately 0.6 to 1.2 milligrams/deciliters (mg/dL) of creatinine, whereas women have between 0.5 to 1.1 mg/dL of creatinine.

Generally creatinine levels in the blood remain unchanged from day to day because muscle mass usually stays the same. Taking certain medicines, eating a lot of meat or building muscles through weight training or other exercise may show higher amounts of creatinine, even in those who do not have chronic kidney disease. Creatinine levels can be lower than normal for people who are elderly, malnourished or are vegetarians.

Creatinine tests

Creatinine in the bloodstream is usually checked with regular tests. There are a few tests which are specifically for creatinine measurement to help determine kidney function.

Serum creatinine is a blood test that is commonly performed as part of a physical examination if have blood work done. Blood is drawn and sent to a lab to be analyzed to find out how much creatinine is in the bloodstream. Serum creatinine helps evaluate kidney function.

Knowing your serum creatinine allows your doctor to calculate your creatinine level along with your age, gender and race, to determine your GFR (glomerular filtration rate). GFR is considered by medical professionals to be the best measure of kidney function. Chronic kidney disease (CKD) ranges from stage 1 CKD (normal to high GFR) to stage 5 CKD (end stage renal disease). If you know a serum creatinine level you can determine the stage of chronic kidney disease using the DaVita GFR Calculator.

Creatinine clearance (Ccr or CrCl) measures how much creatinine is cleared out of the body, or how well kidneys filter waste. Creatinine clearance is a combination of a urine and a blood test. A creatinine clearance test is usually ordered if the serum creatinine level is higher than normal or when a person is starting dialysis. Normal creatinine clearance for men is between 97 to 137 milliliters per minute, and women have a normal clearance of 88 to 128 milliliters per minute.

BUN/creatinine is the ratio between blood urea nitrogen (BUN), a waste product in the blood from protein metabolism, and creatinine. This ratio is used to help determine if kidney function is impaired due to a damaged or diseased kidneys or another factor outside of the kidneys. If both BUN and creatinine are high, the ratio usually indicates damage to the kidneys. If BUN is high but creatinine is normal, then the kidney is generally not damaged but is not getting adequate blood supply due to another problem such as dehydration or heart failure.

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. For adults with chronic kidney disease, dialysis is recommended when creatinine levels reach 10.0 mg/dL. For babies with chronic kidney disease, dialysis is recommended when their creatinine level is 2.0 mg/dL.

Symptoms of too much creatinine

Symptoms of high levels of creatinine in the blood are the same as kidney failure symptoms. Some people find out they have kidney failure when extreme creatinine amounts show up in routine blood tests, without feeling any symptoms at all. Yet some people may experience the following:

  • Weakness, or feeling tired
  • Dehydration
  • Confusion
  • Shortness of breath

When will your creatinine level be tested?

Serum creatinine and BUN/creatinine tests are usually performed during regular blood work. Your doctor may order a creatinine test if he or she suspects your kidneys are impaired. During some drug treatments, your doctor may order frequent creatinine tests to ensure the drug is not harming your kidneys. If you have signs of kidney trouble, your doctor may order a creatinine clearance test.

Nephrologists use these tests to monitor the kidney function of their patients and track the progression of their kidney disease. Doctors also use these tests after a patient reaches end stage renal disease and is on dialysis to check how well dialysis is cleaning the blood.

Summary

Creatinine tests, such as the serum creatinine, creatinine clearance and BUN/creatinine help doctors determine if kidneys are not functioning properly. People diagnosed with chronic kidney disease will likely be tested regularly. Knowing your creatinine level will help your health care team determine your treatment for kidney disease, including the amount of dialysis you should receive.

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