Acute renal failure refers to a sudden loss of kidney function caused by trauma, pregnancy complications, urinary obstructions, serious infections or decreased blood flow to the kidneys. With immediate treatment, some people with acute renal failure regain their kidney function. Others experience long-term effects such as chronic kidney disease, heart damage, high blood pressure and nerve damage. The amount of creatinine in the body varies, based on increases and decreases in kidney function.
Creatinine Production
Creatine, a compound consisting of hydrogen, oxygen, carbon and nitrogen, forms during the breakdown of protein molecules. This substance acts as an energy source for the body, which then breaks the creatine into creatinine. In people without kidney disease or renal failure, the kidneys filter creatinine out of the blood. Acute renal failure impairs kidney function, so the kidneys do not filter creatinine as well as they should.
Serum Creatinine
Checking the amount of creatinine in the blood provides clues as to how well the kidneys work. In someone with acute renal failure, the creatinine test helps determine if someone is regaining kidney function. Using a blood sample taken from one of the veins, a laboratory technician determines the amount of creatinine in one deciliter of blood. Normal creatinine levels range from 0.8 to 1.4 mg/dL Acute renal failure causes a sudden increase of at least 0.5 mg/dL from the patient's normal creatinine level, according to the American Academy of Family Physicians.
Creatinine Clearance
The creatinine clearance test also helps monitor the status of someone with acute renal failure. This test compares the amount of creatinine excreted in the urine to the amount of creatinine in the blood. A phlebotomist takes a blood sample to determine the amount of creatinine in the blood. The patient collects her urine for 24 hours so the laboratory can determine how much creatinine is in the urine. Using both samples, a laboratory professional determines the rate of creatinine clearance. Normal creatinine clearance ranges from 88 to 128 ml/min for women and 97 to 137 ml/min for men. Patients with acute renal failure have lower creatinine clearance rates.
BUN-to-Creatinine Ratio
When the liver breaks down protein molecules, it produces ammonia. The nitrogen in the ammonia combines with other elements to form a waste product called urea. Normal kidneys filter this waste product from the blood, but impaired kidneys cannot filter urea effectively. This allows the nitrogen from the urea to build up in the bloodstream. The BUN-to-creatinine ratio compares the amount of blood urea nitrogen in the blood with the amount of creatinine in the blood. People with normal kidney function have BUN-to-creatinine ratios between 10-to-1 and 20-to-1. People with acute renal failure have ratios above 20-to-1.
