Serum Creatinine vs 24-Hour Creatinine Clearance (Pre-D)

[KarenInWA]

My neph ordered a 24-hour urine collection back in August.  As of late, my serum creatinine has been hovering around 2.1, w/a GFR of 27, down from a previous 29 and 33 (with serum c being 1.9 - 2.0).  Upon getting the results, my GFR was 27, and my 24-hour one showed kidney function of 36.  He then tells me that they go by the serum one, because it's "more accurate".

Fast fwd to a recent trip to the primary care doctor (I go to a clinic with multiple docs, so she was not my "normal" one) for gawd-awful intestinal issues from Hell, and I bring this up to her.  She looked at those labs from August, and mentioned that the 24-hour one is the more accurate one, and that the serum one is more of an estimate.  After all, why go through all the hassel of collecting your pee for 24 hours if it's not going to give you a "better" reading?  She has a point, I think, as well as the fact that the kidneys produce urine.  Oh, that's right, they filter blood, too. 

Also, I do remember our dear friend Richard telling me the same thing along those lines about the 24-hr collection, and I figure he's been going thru all this longer then I have.  So, what do you all think?  I'd feel much better being in Stage 3, rather than Stage 4.

Thank you, everyone, and please, stay away from intestinal viruses/bacteria, or whatever hell has taken over my body.  Blech!!!

KarenInWA

[kristina]

Years ago I was told that a 24-hour-urine-collection

is not necessary anymore in ESRF

and that is why it was not done.

My kidneys still function ~10%

and I wonder if I was given the right information?

[RichardMEL]

kristina there is a difference though. You mention ESRF - KarenINWA is not in end stage yet (hooray!). Certainly I have not done a 24 hour collection since I started dialysis - but then again I don't output enough to make a dent in one of those bottles! However again I was always told that the 24 hour test was more accurate in measuring kidney function, creat levels etc because it accounted for the variations of diet and intake and the like in a day, whereas the serum creat level was a point in time estimate from a sample of blood.

Now I am sure Zach or Kidneydoc would have a more reliable opinion than me, but I think yes - the 24 hour collection is more accurate.

36% is a very good figure, and your creat is not that much higher than a post transplant kidney - so you're clearly still doing very well - which is fantastic to read!!!

 

[BrandyChloe]

I've known about my kidney issues for 30 years but they are just now at the point of being labeled stage 5. Back in May of this year, the neph had me do another 24 hour collection to be certain it was "time" to start the dialysis/transplant process. The GFR from my blood work was 17% but the GFR from my urine collection was 27%. I asked why the big difference and he told me the urine numbers were the more accurate but the blood numbers is what the medical community uses to determine your kidney status.

I haven't done another collection since then but I don't guess it really matters because my GFR has dropped 1% a month since May and I am now reading at 12% so regardless, it was time for me to start the dialysis/transplant process.

[kristina]

Thanks for the information, Richard,

it is very much appreciated.

[Hanify]

I am on PD and every three months I have to do a 24 hr urine collection so they can include this with the output of my bags and check how it's going.  The funny ting is that the 24 hr urine collection is all of about 200ml (a cup) so I can take it in in a tiny takeaway container ha ha.  Gone are the days when I need a huge 3 l container.  I can't even imagine peeing that much lol.  Anyway, my point is they still also do the serum tests as a separate thing.

[del]

About a year after hubby started hemo he was told they needed a 24 hour urine. He told them he didn't pee. Didn't make any difference the docs wanted it.  he took the bottle home and the nurses all laughed when he brought it back.  they asked him how many times he had to shake to get the little dribble in the bottom of the bottle.  LOL!!

[Jie]

It is sad to read these posts. There are so many medical professionals out there who do not know what is the good measurement of the kidney functions. The 24-hr urine collection always overestimates the kidney functions.  This conclusion has been made at least several years ago, since the MDRD study. Right now, it seems every center is using the serum creatinine to estimate kidney function through the formula. Even though the serum creatinine method is an estimate, its formula is based on the accurate measurement of the kidney functions, which are measured through 24-hr urine collection with some INJECTION.  Without the injection, the 24-hr urine collection is overestimating the kidney functions.

When one is healthy, the clearance rate from the 24-hr urine collection is about 80% from kidneys and 20% from others.  So for a healthy person or close to healthy person, 24-hr urine collection is a reasonable measurement of kidney functions. When one's kidney function is about 20%, the clearance rate from the 24-hr urine collection could be 50% from the kidney and another 50% from others. This is the reason for the overestimates.  For PD patients, when one has fair amount of urine, the Kt/V may be also overestimates (this is my guess, not based on any study) because it takes an average of clearance rate and another measurement as a residual kidney function. The average is always lower than the clearance rate, a step at the right direction, but I am not sure it has lowered the clearance rate enough to truly reflect the residual kidney functions.

The bad consequence for this mistake of many medical professionals is a delay for a patient to start the transplant evaluation and get into the waiting list. I was delayed by my neph's mistake for close to one year. I am sure a lot of patients would be delayed longer than I did.  I found this out and pushed very hard to my neph to refer me for transplant evaluation.