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  #1  
Old 07-24-2011
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Kidney What changes expected in the GFR

A critically ill, 17-year-old girl was unable to take food orally. She was found to be in a catabolic state, with accelerated breakdown of skeletal muscle. Her steady-state daily creatinine production rate increased from 600 mg/day to 1200 mg/day. Over the same period, plasma creatinine concentration increased from 1 mg/dL to 2 mg/dL. From these data, what can be concluded about changes in her glomerular filtration rate (GFR) over this period?

A. GFR did not change
B. GFR doubled
C. GFR halved
D. GFR was zero
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Old 07-24-2011
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GFR does not depend on creatinine concentration, so my answer is A..
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Old 07-24-2011
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C)gfr is halfed
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Old 07-24-2011
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i think C. GFR halfed??
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Old 07-24-2011
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My answer is C creatinine clearance predicts GFR here plasma concentration of creatinine is doubled so its clearance must reduce by half so GFR is halved
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Old 07-25-2011
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i think A coz we know creatinin is not a very excellent predictor for GFR coz it can change with changes in muscle mass and now u r playing with the production not with the clearance so if it doubled the clearance would almost be doubled but the GFR i wont change
waiting for the correct answer
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Old 07-25-2011
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I think it's A, since patient's creatinine is high due to intense skel muscle breakdown, not to the decreased GFR.
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Old 07-25-2011
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Default A.

should be A.
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Search correct answer

The correct answer is A- GFR did not change.

To match the doubled creatinine production rate, renal excretion rate also doubles. Renal creatinine excretion rate is approximately the product of GFR and plasma creatinine concentration. If GFR were unchanged and creatinine production doubled, then plasma creatinine would rise to two times normal, as shown by the data.

If GFR were half of normal and creatinine production doubled, then plasma creatinine would rise to four times normal. The data show only a doubling of creatinine.
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Old 07-25-2011
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Default A

No change in GFR
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I think A. at steady state creatinine production equals creatinine excretion. Creatinine production = creatinine concentration* GFR. Therefore, GFR=creatinine production/creatinine concentration. Everything doubled, so the answer is A - did not change.
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Post A

A. GFR did not change
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Default

Quote:
Originally Posted by bebix View Post
The correct answer is A- GFR did not change.

To match the doubled creatinine production rate, renal excretion rate also doubles. Renal creatinine excretion rate is approximately the product of GFR and plasma creatinine concentration. If GFR were unchanged and creatinine production doubled, then plasma creatinine would rise to two times normal, as shown by the data.

If GFR were half of normal and creatinine production doubled, then plasma creatinine would rise to four times normal. The data show only a doubling of creatinine.
(600-E)/V=1 -> E=600-V
(1200-E')/V=2 -> E'=1200-2V

E=GFR*1 -> GFR=600-V
E'=GFR'*2 -> GFR'=600-V

GFR=GFR'

A is correct.
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