Creatinine is a chemical waste product that is released into the blood when muscles contract. When kidney function is normal, creatinine is filtered from the blood through the kidneys. When creatinine levels are high, it can be an indicator of kidney disease. For adults, dialysis is recommended when creatinine levels reach 10.0 mg/dL; for children, dialysis is recommended when levels reach 2.0 mg/dL. To find out what a person’s creatinine levels are, a doctor will order a blood test called serum creatinine to determine kidney function and use the number to calculate the glomerular filtration rate (GFR), which can determine the stage of chronic kidney disease.

Doctors perform two other tests to determine creatinine levels: creatinine clearance (Ccr or CrCl) and BUN/creatinine. Creatinine clearance is a combination of a blood and a urine test, which measures how much creatinine is cleared out of the body, or how well kidneys filter waste. The test may be ordered by the doctor if a person shows signs of kidney problems or is going to start dialysis. 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 damaged or diseased kidneys or another factor outside of the kidneys. The serum creatinine and BUN/creatinine tests are usually performed during regular blood work. When a person has kidney disease, his or her doctor will continue performing creatinine tests to monitor the disease’s progression and to determine the person’s kidney disease treatment.

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