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Any thoughts or comments (or references) on which parameter, serum
creatinie or seum BUN, is a more sensitive indicator of decreasing
renal function in humans?
Thank
Dave
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SCr is regarded as much more sensitive than BUN
in the literature. Another measure of incipient
decline in renal function is the Spot Urine Micro
test, I believe.
I believe that the Kidney Foundation (Dr Levey)
has recommended use of Cystatin-C over SCr as a
proxy for GFR, glomerular filtration rate. --
SCr is known to have limitations as a measure of
renal function for certain populations -- those
whose actual body weight it much greater than
ideal body weight, for example, and there are other
situations where it is known not to work well.
There are many papers in the literature regarding
estimation of GFR using either SCr or Cystatin-C.
Paul Robertson
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Dave:
The quick answer is neither although that is a vast
oversimplification. BUN may be affected by a variety of factors
including protein metabolism/catabolism so it is less specific for
renal function compared to serum creatinine, it also may lag behind
creatinine in representing changes in creatinine.
Using serum creatinine to estimate creatinine clearance tends to
overestimate renal function especially in the elderly and those with
smaller body mass.
there are a variety of formulas that do a better job of estimating
renal function compared to serum creatinine in humans including:
Levey's, Walser's and Cockroft-Gault. Some of these formulas aren't
very practical so the best choice of methods really depends upon your
intended use.
A few potentially useful references:
Scand J Urol Nephrol 2004;38:73
J of Gerontology 1976:31:155
Br J Clin Pharmacol 2007;63:509.
Sincerely,
Carol Collins MD
University of Washington
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Hi Dave,
BUN is a somewhat more sensitive indicator of compromised renal
function since it tends to increase before creatinine does. On the
other hand, it's readily affected by dietary protein intake.
There are more marked sex differences with creatinine (higher
creatinine concentrations in males, especially in "body builders").
The clearance of creatinine has been more extensively studied in the
context of water soluble drug clearance and can be readily estimated
by a single serum creatinine level using the Cockcroft-Gault
equation. Dr. Jelliffe on this list has published several articles
relating to this topic.
- Peter
Peter W. Mullen, PhD, FCSFS
KEMIC BIORESEARCH
Kentville
Nova Scotia, B4N 4H8
Canada
Email: pmullen.at.kemic.com
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The following message was posted to: PharmPK
Hi, Dave.
If you under "decreasing renal function" mean "decreasing glomerular
function" many authors today
suggest cystatin C as the most sensitive indicator for this disorder.
It should detect 20% decrease
in glomerular function. The second best choice would be creatinine
clearance (the measured, not the
estimated one). It should detect 40% decrease in glomerular function.
Finally, among the
alternatives you proposed I would choose serum creatinine. For
example, highest BUN values you will
find in GI bleeding. There are numerous other causes of high BUN
values. There are many causes of
serum creatinine increase/decrase other than glomerular insufficiency,
also. If you want to
differentiate between different causes of creatinine and BUN increase
you could consider their
ratio. Some authors suggest to use urea clearance for assessing
glomerular function when it falls
bellow 20%, but I suppose you are not interested in terminal
insufficiency. More details you can
find in different clinical chemistry textbooks like "Clinical
Laboratory Diagnostics" by Lothar
Thomas or "Tietz Textbook of Clinical Chemistry" etc. Hope this helps.
Zeljko Debeljak, PhD
Medical Biochemistry Specialist
Clinical Hospital Osijek
CROATIA
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Inulin and PAH clearances are more controlled and better indicators of
renal excretory function.
--
Ed O'Connor, Ph.D.
Laboratory Director
Matrix BioAnalytical Laboratories
25 Science Park at Yale
New Haven, CT 06511
Web: www.matrixbioanalytical.com
Email: eoconnor.-a-.matrixbioanalytical.com
[Inulin for GFR and PAH for renal blood flow? - db]
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Serum Creatinine is useful for 'normal' relatively healthy patients.
BUT it can be extremely misleading in several subsets of the
population. Since it is closely tied to muscle mass patients' muscle
vs fat ratio needs to be checked for deviations from the norm - e.g.
elderly and infants are biased away from muscle mass.
Where you can really get into trouble with serum creatinine is the
patient population who have compromised renal function. Their kidneys
accomodate the increased creatinine levels with an upregulation of an
alternate excretion path... the details of which escape me at the
moment.... and their renal function can bear very little relationship
to serum creatinine levels as predicted by normal calculations...
especially when they are acutely ill or in acute renal failure.
You also have to watch for hydration status... with dehydration being
a common condition across the population and especially in the
elderly... and this will cause high serum creatinine levels... the way
to check for this is to evaluate the BUN to Serum Creatinine ratio.
Details of this can be found in many textbooks.
hope this was useful
steve mitchell
clinical pharmacist
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