I have hard time understanding and memorizing table with FENa %, BUN:Cr ratio, UNa and UOsm. 2 sources I used (RR Path - Page no 407 and FA 2011 Page no 471) have written different values and contradict in some sense.
Please make me understand this table. I get such questions wrong many times.
In advance, thanks a lot.
Prerenal: FENa - Low blood flow into the kidney, therefore your kidneys try to reabsorb more and you get increased Renin system so you reabsorb more Na therefore, FENa (Fraction Excreted Na) is LOW (its all being reabsorbed from the kidney).
BUN/Creat - Urea gets BOTH filtered and reabsorbed whereas Creatinine is mainly filtered. Low blood flow into the kidney increases BOTH Urea and Creatinine (less can be filtered) but since the Renin system is upregulated too then you get INCREASED resorption of urea in the prox tubule. Therefore BUN/Creat is HIGH since Urea is increasing more than creatinine.
Uosm - Renin system is high so you reabosorb alot of solute and water in the prox tubule leading to a more concentrated urine.
Renal: FENa - There is intrinsic damage to the kidney so it cannot function. Therefore you cannot reabsorb stuff and everything gets peed out. FENa is high.
BUN/Creat - Since you cannot reabsorb urea the BUN/Creat is low/normal.
Uosm - Since you aren't reabsorbing anything you are peeing out both solute and water so urine is relatively dilute.
Post-renal: Depends on if it is chronic or acute. Most likely wont be on the exam and if it is just know that it only really happens if there is bilateral obstruction of the ureters since if its only on one side, the other kidney will make up for the losses.
Also - UNa is the same as FENa (FENa is a % and UNa is an ammount)
Sorry if there are typos.
