1. Why do I have to collect my urine for 24 hours?
A 24-hour urine sample is required instead of a random urine sample because the amount of creatinine in the urine will vary somewhat during the course of a day. By collecting all urine for 24 hours, the amount of creatinine in the urine can be averaged over the entire day and will give a better indication of what is going on in the body.
2. What should I do if I forget to save one urine sample during the collection?
If you do not have a complete collection, the results will not be valid. You should call your doctor's office or the laboratory where you obtained your collection container to ask if you should discontinue the test and begin again another day.
3. Are there other ways to estimate or determine the Glomerular Filtration Rate (GFR) of my kidneys?
Yes. The GFR can be estimated using the result of a blood creatinine test and a calculation. (See the article on eGFR). Collection of a 24-hour urine specimen can be prone to errors. A reasonable estimate of actual GFR can be calculated based on serum creatinine, a common test that is easily performed.
Also, there are other, more involved tests that have higher accuracy than a creatinine clearance. However, these involve injecting the patient with a tracer and are more expensive. For most clinical purposes, the accuracy of creatinine clearance is sufficient.
This article was last reviewed on November 29, 2012. | This article was last modified on November 29, 2012.
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