Creatitine Clearance Test Accuracy

[Rog210]

I am being considered as a kidney donor and have recently undergone a creatatine clearence test.  It showed a very low level of clearence 65 and I was turned down.  Surprised I did some reading.  This test is the ratio of blood creatitine to urine (24 hr) creatitine.   Since my blood and urine were taken weeks apart I questioned the validity of the test.  I ask for a my doctor to retest me and got and the second test, with blood drawn at the end of the urine collection period, showed a value of 108.  I was not surprised there was a difference because the blood for the first test was drawn at time when I was poorly hydrated.  (For the first urine test and the second blood and urine I had normal hydration.)  

For me this indicates not just a problem with the kidney donor group (they should have requested matched blood and urine), but with the lab (they should not have reported results based on unmatched blood and urine samples).  So I called a nephrologist and was told it is not uncommon for blood and urine samples to be weeks apart.   How does this make sense since both can be impacted by the patient's hydration level?

[veggiemom1436]

Gosh, I'm notorious for serial posting, but I just wanted to validate the point you are making.  My serum creatinine was 0.68 the day I dropped my urine off.  The following day it was 0.74 (taken for another purpose).  2 months prior, it was 0.8.  It obviously fluctuates, even daily, and that is precisely why they do the timed collection.  I'm sorry you were turned down the first time - I'm assuming that they have now approved you?  

[veggiemom1436]

From everything I've read (and trust me, with my problems I've been reading a lot), and everything the lab tech told me, the serum creatinine MUST be drawn either within the 24 hours before the test or within the 24 hours after the test.  I dropped my urine off 4 hours after completion and it was drawn then and there.  The way they did your CrCl makes no sense!  The whole purpose of doing a CrCL is a TIMED collection.