This test measures the concentration (amount per volume) of creatinine in both a sample of blood and a sample of urine from a 24-hour urine collection. Creatinine is a protein from muscle, made constantly by the body, filtered freely by the kidney (freely passed into the urine without obstacle) and excreted (removed from the body, in this case in the urine) daily. The results are used to work out how much creatinine has been…This test measures the concentration (amount per volume) of creatinine in both a sample of blood and a sample of urine from a 24-hour urine collection. Creatinine is a protein from muscle, made constantly by the body, filtered freely by the kidney (freely passed into the urine without obstacle) and excreted (removed from the body, in this case in the urine) daily. The results are used to work out how much creatinine has been cleared from the blood and passed into the urine. This number reflects how much blood is being passed throughthe filtering part of the kidneys (the glomeruli) in a 24-hour time period. The amount of blood filtered per minute is known as the Glomerular Filtration Rate (GFR). If the glomeruli are damaged or diseased, or if blood circulation is slowed, then less creatinine will be removed from the blood and the GFR will drop. As creatinine levels tend to remain the same in a person a single creatinine measurement fromthe blood can be used to assess GFR when combined with the creatinine found in the urine collected over a period of time. How is the sample collected for testing? The test requires a 24-hour urine collection and a blood sample taken either at the beginning or end of the urine collection. The blood sample is collected by needle from a vein in the arm. Is any test preparation needed to ensure the quality of the sample? No test preparation is needed but heavy exercise should be avoided to prevent falsely high readings. Protein supplements should also be avoided during the test as they contain creatinine. You should drink as normal with no other change to your routine or habits. See MoreSee Less
