Creatinine vs. BUN: Hello everyone from a... - Early CKD Support

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Creatinine vs. BUN

Alex6157
Alex6157

Hello everyone from a new group member.

Could people here share with the rest of us their experience with the dynamics of Creatinine (or GFR) and Blood Urea Nitrogen? I wonder whether BUN usually goes up when creatinine does so, or can stay normal (between 7 and 20) throughout earlier stages of ckd. Here are my averages year to year:

2013: GFR 87, BUN 15

2014: GFR 56, BUN 19

2015: GFR 65, BUN 14

2016: GFR 62, BUN 14

2017: GFR 60, BUN 14

2018: GFR 61, BUN 14

2019: GFR 55, BUN 15.

10 Replies
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Okay, lets try to understand this a little. BUN (Blood Urea Nitrogen). The liver produces this waste product as it breaks down proteins. It carries in your blood stream. The kidneys filter this waste, leaving only "normal" amounts in your blood. Creatinine is produced by your muscles. The normal daily wear and tear on muscles (or exercise) produces it. It carries in your blood. Your kidneys filter this out and leave only "normal" amounts in your blood. These are both measured in a blood test. There is a third important test. The BUN/Creatinine Ratio. My doctors advise me to them this is even more important to their study, than even eGFR. As it reflects a direct measurement of how well the kidney is filtering. Both are affected by various things. Such as dehydration. Obviously kidney disease. Diet. etc. Now can one be high and the other lower (example high BUN, normal Creatinine)? Yes. Can you have high creatinine and "normal" BUN, yes. But in a "normal" functioning kidney and liver, there is a range of BUN/Creatinine that indicates the performance. Now, your egfr has nothing to do at all with your BUN level. It only considers Creatinine. You also ask about the relationship compared to the stage you are in. You can be in a stage and have normal BUN and high Creatinine.

Now about your numbers. A change in your eGFR is normal. It can change up or down from blood test to blood test, because of your Creatinine level, or you become a year older (the formula for determining eGFR considers your age), dehydration, medications, other illnesses, etc. Notice the change in yours from 2014 to 2015. But see how constant your BUN level stays. You will see on here a lot of debate on if a person such as yourself even has kidney disease. That is the egfr process valid? that if your BUN is normal, your urine tests are normal, any scans are normal, then what is giving you a lower than "normal" egfr?? It is really a kidney problem or does you body just produce a creatinine level that is above the "normal" range. The benefit of egfr is just to monitor it over time. Do you remain in a study range (up or down only a few points). From all indications you are doing so.

Alex6157
Alex6157
in reply to RickHow

Thank you for your very informative response, RickHow. Yes, eGFR is based only on creatinine (plus age, gender and race). But I found some earlier formulas had BUN as one of their variables. Here is one:

medcalc.com/gfr.html

Jonquiljo
Jonquiljo
in reply to Alex6157

They don't use any old formulas when checking GFR. There is the MDRD which is not reliable for GFR's over 60 - so you can get ">60" on your test results (not very helpful!). There's the CKD-EPI calculation method which is now supposedly more reliable, but again it uses only creatinine and age.

As Rick said, BUN/Creatinine is very helpful. Also, if you want to get an even better metric - have them give you a cup and check urine Albumin or urine Albumin:Creatinine (aka "ALC"). If you have an "ALC" that is below 30 (mcg/L?) - you are very normal and it is not that likely that you have any kidney damage. This is all about kidney damage after all.

So many people come on here and their Drs do not do anything but give them blood tests. Processing urine is relatively cheap and easy and reliable. It tells you a lot! Good luck.

RickHow
RickHow
in reply to Jonquiljo

Yep, I too should have mentioned al/creatinine urine ratio. My oncologist concentrates all her attention to this result above all others. She is in an office of 4 oncologists. She said they all virtually ignore eGFR for patients with kidney related problems. First they check al/creat, then bun/creat. She says this tells her the majority of the information that is needed (of course protein, etc), but not eGFR.

Alex6157
Alex6157
in reply to Jonquiljo

Thanks!..

vinadhun2
vinadhun2
in reply to RickHow

I found your comments very interesting.

I am 73 year old male.i have no health issue.i do not have protein in urine. All values are normal including electrolytes and BUN etc.

Only creatinine is elevated to 1.74.so I presume that I do not have kidney disease.my creatinine is slightly elevated.

By the way even other marker namely Cystatin C is also normal at 1.18

Any opinions

RickHow
RickHow
in reply to vinadhun2

Yes you are doing fine I think. Also don't forget that as we age it is typical for our kidneys to "weaken". In your case and mine we are in our 70's. Those kidney's have been filtering for 70+ years. So some elevation in numbers is expected. That is why formulas that take into consideration your age, when calculating kidney function, are far superior to the "normal" method which only calculates creatinine, sex, race. For example I can get the "normal" egfr, with my creatine level and be called Stage 3b. But I run the same numbers through a formula that considers age, and I just to borderline stage 2.

vinadhun2
vinadhun2
in reply to RickHow

Can you give formula being used by you

BUN shows how well your body is filtering out wastes. I look at it as showing me whether I am drinking enough fluids or not. If my BUN is up, I know that I am dehydrated. There is a definite relationship with creatinine. When my BUN is abnormal, my creatinine will also be up. So dehydration really effects your kidney function. I have had a transplant and this is still true for me.

So you can also imagine that eGFR is an estimate of how well your kidneys are filtering. So if your BUN is elevated you know that will also effect your GFR - all effected by not drinking enough.

That said, when your CKD advances GFR, BUN and creatinine are all elevated above normal levels. Don't know what my GFR was, but when I had my transplant my daily BUN was 55 with a creatinine of 4.7.

Hope this helps some. If my creatinine is up from where it normally is, my nephrologist looks at my BUN.

Alex6157
Alex6157
in reply to WYOAnne

Thank you, WYOAnne. The info you provided is helpful.

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