Creatinine and creatinine clearance tests

You may be asked to:

• Not do any strenuous exercise for 2 days (48 hours) before having the tests.
• Not eat more than 8 ounces of meat, especially beef, or other protein for 24 hours before the blood creatinine test and during the creatinine clearance urine test.
• Drink plenty of fluids if you are asked to collect your urine for 24 hours. But don't drink coffee or tea. These are diuretics that cause your body to pass more urine than normal.

If you are asked to collect urine, your doctor will give you a large container that holds about 1 gallon. You will use the container to collect your urine for 24 hours.

Tell your doctor ALL the medicines, vitamins, supplements, and herbal remedies you take. Some may increase the risk of problems during your test. Your doctor will tell you if you should stop taking any of them before the test and how soon to do it..

These tests give information about how well your kidneys are working. The creatinine clearance value is found from the amounts of creatinine in the urine and blood and from the amount of urine you pass in 24 hours. This value is the amount of blood cleared of creatinine per minute, based on your body size.

Each lab has a different range for what's normal. Your lab report should show the range that your lab uses for each test. The normal range is just a guide. Your doctor will also look at your results based on your age, health, and other factors. A value that isn't in the normal range may still be normal for you.

Blood creatinine, creatinine clearance, and BUN-to-creatinine ratios can be measured.

• High creatinine blood levels can be caused by:
  • Serious kidney damage or chronic kidney disease. Kidney damage can be caused by a life-threatening infection, shock, cancer, or low blood flow to the kidneys.
  • Dehydration.
  • Muscle injury and conditions. These include crush injuries, burns, rhabdomyolysis, muscular dystrophy, polymyositis, and strenuous exercises.
  • Shock. This is low blood pressure with many causes including severe bleeding and very severe infection.
• High creatinine clearance levels can be caused by carbon monoxide poisoning and pregnancy.
• High BUN-to-creatinine ratios occur with sudden (acute) kidney problems. This may be caused by shock or severe dehydration. A very high BUN-to-creatinine ratio may be caused by bleeding in the digestive tract.

• Low blood creatinine levels can mean lower muscle mass caused by a disease, such as muscular dystrophy, or by aging. Low levels can also mean some types of severe liver disease or a diet very low in protein. Pregnancy can also cause low levels.
• Low creatinine clearance levels can mean you have chronic kidney disease or serious kidney damage. Kidney damage can be from conditions such as a life-threatening infection, shock, cancer, low blood flow to the kidneys, or urinary tract blockage. Other conditions, such as heart failure and dehydration, can also cause low clearance levels.
• Low BUN-to-creatinine ratios may be linked with a diet low in protein, a severe muscle injury called rhabdomyolysis, pregnancy, cirrhosis, or syndrome of inappropriate antidiuretic hormone secretion (SIADH). SIADH sometimes occurs with lung disease, cancer, diseases of the central nervous system, or the use of certain medicines.