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Creatinine and Creatinine Clearance

What Affects the Test

Reasons you may not be able to have the test or why the results may not be helpful include:

  • Taking medicines, such as methyldopa, trimethoprim (Proloprim, Trimpex), vitamin C (ascorbic acid), cimetidine (Tagamet), some diuretics, and cephalosporin antibiotics, especially cefoxitin (Mefoxin). These affect the blood creatinine levels.
  • Taking medicines, such as vitamin C (ascorbic acid), phenytoin (Dilantin), some cephalosporin antibiotics, captopril, aminoglycosides, trimethoprim (Proloprim, Trimpex), cimetidine (Tagamet), quinine, quinidine, procainamide, and the antifungal medication amphotericin B. These affect the creatinine clearance levels.
  • Taking medicines, such as cimetidine (Tagamet), steroids, and tetracycline antibiotics. These can affect the BUN-to-creatinine ratio.
  • Not collecting all your urine during the 24-hour urine collection test.
  • Doing strenuous exercise 2 days before creatinine clearance test.
  • Eating more than 8 oz (227 g) of meat, especially beef, in the 24 hours before a blood creatinine test and during a creatinine clearance urine test.

What To Think About

  • A high blood creatinine level is generally seen with a low creatinine clearance level because creatinine in the blood is normally removed by the kidneys. If the kidneys are not able to remove creatinine (low creatinine clearance), levels of creatinine in the blood go up (high blood creatinine level).
  • If you are pregnant, your doctor can check the amount of creatinine in amniotic fluid to see how developed, or mature, your baby's kidneys are. This can be helpful if there is a chance your baby will be delivered early. A baby who has mature kidneys will make more creatinine than a baby whose kidneys are still developing.
  • A normal blood creatinine level does not rule out kidney disease. To help see whether kidney damage may be present, creatinine clearance is also measured. Other tests may also be done to check for kidney disease. For more information, see the topic Blood Urea Nitrogen.
  • Creatinine levels increase more slowly than blood urea nitrogen (BUN) levels, so an increase in creatinine may mean chronic kidney problems.
  • A glomerular filtration rate may be done for people with chronic kidney disease to regularly check how well the kidneys are working.
  • Diabetes experts recommend that blood creatinine levels be done every year for people with diabetes. The creatinine level is used to find the glomerular filtration rate, which shows how well the kidneys are working.
  • The amount of creatinine in the blood depends partly on the amount of muscle tissue; blood creatinine levels are generally higher in men than in women. Also, people who have large muscles, such as athletes, normally have above-average blood creatinine levels.
  • A one-time urine sample to measure urine creatinine and sodium is sometimes done along with blood creatinine and sodium levels to help find the fractional excretion of sodium (FENa). This test can help your doctor see whether a problem with blood flow to the kidneys is caused by dehydration or shock or by damage to the kidneys themselves.

WebMD Medical Reference from Healthwise

Last Updated: August 09, 2012
This information is not intended to replace the advice of a doctor. Healthwise disclaims any liability for the decisions you make based on this information.

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