Creatinine and creatinine clearance tests are used to measure the level of the waste product creatinine in the blood and urine of the patient. These tests provide information about how well kidneys are working. Creatine is formed when food is transformed into energy through a process of metabolism. Creatine is broken down there into another substance – creatinine, which is taken out of the blood with the help of the kidneys and then is driven out of the body with urine.
Creatinine is forming at a steady rate and can not be affected by any diet or normal physical activities. If your kidneys are impaired and cannot function normally, the quantity of creatinine in urine goes down but at the same time it increases in the blood.
A creatinine clearance test gives more precise information on how well kidneys are working. A creatinine clearance test is done on the basis of both a blood and urine samples. Sample of urine is to be collected over 24 hours.
Usual normal results of the test:
Men: 90–140 milliliters per minute (mL/min) or 1.78–2.32 milliters per second (mL/sec)
Women: 87–107 mL/min or 1.45-1.78 mL/sec
If you are going to take the mentioned test you should make some preparation beforehand. Do not do any physical exercise for 2 days (48 hours). Do not eat more than 8 oz of meat, especially beef, or other protein for 24 hours before. It is important to drink enough fluids during the 24-hour urine collection but do not drink coffee and tea. These are diuretics that cause your body to pass more urine.