The creatinine test measures creatinine concentrations in both the blood and the 24-hour urine sample. The results are used to calculate the concentration of creatinine that passes from the blood to the urine. This calculation allows for a general assessment of the amount of blood that is filtered by the kidneys over a period of 24 hours.
Creatinine is a muscle waste product that comes from a molecule called creatine. Creatine is part of a metabolic cycle that produces energy needed for muscle contraction. The amount of creatinine produced depends on the physical size of the individual and his muscle mass, and is relatively constant.
Almost all creatinine is removed from the body by the kidneys; the concentration in the blood is a good indicator of how the filtering units of the kidneys, the glomeruli, work. The concentration of creatinine removed from the blood depends on both the filtering capacity of the renal glomeruli and the speed with which the blood is transported to the kidneys.
The amount of blood filtered per minute is called the Glomerular Filtration Rate (GFR). If the glomeruli are damaged or affected by pathologies, or circulation is slowed down, then less creatinine from the blood is removed and released into the urine, and the GFR decreases.
There are several versions of the creatinine clearance calculation. All include the measurement of the amount of creatinine in the blood sample taken immediately before or immediately after the urine collection, the concentration of creatinine in the urine over 24 hours and the volume of urine over the 24 hours. Since the concentration of creatinine produced depends on muscle mass, some calculations use a correction factor that takes into account the body surface area (using weight and height).
Creatinine is a muscle waste product that comes from a molecule called creatine. Creatine is part of a metabolic cycle that produces energy needed for muscle contraction. The amount of creatinine produced depends on the physical size of the individual and his muscle mass, and is relatively constant.
Almost all creatinine is removed from the body by the kidneys; the concentration in the blood is a good indicator of how the filtering units of the kidneys, the glomeruli, work. The concentration of creatinine removed from the blood depends on both the filtering capacity of the renal glomeruli and the speed with which the blood is transported to the kidneys.
The amount of blood filtered per minute is called the Glomerular Filtration Rate (GFR). If the glomeruli are damaged or affected by pathologies, or circulation is slowed down, then less creatinine from the blood is removed and released into the urine, and the GFR decreases.
There are several versions of the creatinine clearance calculation. All include the measurement of the amount of creatinine in the blood sample taken immediately before or immediately after the urine collection, the concentration of creatinine in the urine over 24 hours and the volume of urine over the 24 hours. Since the concentration of creatinine produced depends on muscle mass, some calculations use a correction factor that takes into account the body surface area (using weight and height).
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