Help with Patho of BUN and Creatinine in CHF

cupcake231 · May 15, 2010

I believe that BUN levels would be increased during CHF because during CHF, bloodflow to the kidneys is reduced and therefore making BUN high. I am not sure about the creatine though...

RNTutor, BSN, RN · May 15, 2010

That's a great question!! I'm a big nerd, but I get excited when nursing students ask questions that show they are thinking about the 'why' and not just trying to memorize the what.

In order to answer this question, think about HOW the creatinine test is done. There are 2 ways: blood test, or urine. Since you stated that it's related to GFR, then that makes me think you are talking about the urine version, which is the Creatinine Clearance test (CrCl).

The CrCl measures how much creatinine is in a 24-hour urine sample. That result tells you what the GFR is, because it it means that the glomeruli are able to filter that much creatinine/24hrs. So if the Cardiac Output is decreased, then the GFR is decreased, which means that less creatinine is excreted into the urine. Ta-da! A decreased CrCl as a result of CHF.

Now, Creatinine tends to rise in the blood slower than BUN does, so if Creatinine is high in a blood test, then it probably indicates a chronic disease (such as in the case of CHF). But Creatinine tests and BUN are almost always interpreted in relationship to each other anyway, because each one is influenced slightly differently by different diseases.

So short answer is that serum creatinine would probably be high, but Creatinine Clearance measured in the urine would be low since the kidneys just can't get it out of the body.

Hope that helps!

dinhm17 · May 18, 2010

Great! Thanks for clearing that up for me. I checked my lab book and it does make that distinction about creatinine clearance. Now my mind can rest easy about that :).

lvaliav · May 18, 2010

good explanation! =)