Renal and Pre-renal failure : differences

                                    pre-renal                renal

fractional    
Na excretion           <1%                         > 2%

Urinary Na               <20                           > 40

Urine osmol              > 500                      < 350

Creatinine                 > 40                       <20



In pre-renal cause, the kidney itself has no pathology but loss of function of kidney is due to decreased perfusion of kidney. Eg. Shock, hypovolaemia, hypotension, bleeding.
Incontrast in renal cause, there is primary pathology in kidney which cause loss of kidney function.

Fractional Na excretion is the fraction of sodium filtered by kidney excreted in urine.

Fraction Na excretion: In pre renal cause, the tubular epithelium is functionalmn it can reabsorp the Na and can concentrate the urine. Therefor fractional Na excretion is low, urinary Na is low and urine osmolality is high.


blood urea and creatinine:
        Creatine is not reabsorped in tubules. whatever filtered by kidney is excreted.
  In pre-renal, there is decrease in GFR~ decrease creatinine excretion and hence creatinine accummulate in body.

urea is increased due to two reason:
            1.) Decrease in GFR directly cause decrease in urea excreation.
             2.) Due to decreased GFR, proximal tubule gets more time to reabsorb filtered urea.
             
so there will be disproportionate increase in creatinineand urea in pre-renal kidney failure.





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