Postrenal acute renal failure

Patients with prerenal azotemia have urinary sodium levels of less than 20 mEq/liter, consistent with normal tubular function. In contrast, patients with either acute renal failure or postrenal azotemia have urinary sodium levels greater than... 

Table 19.1. The most common causes of acute renal failure with regard to the major pathogenetic mechanisms perirenal causes, intrinsic renal failure and postrenal etiology (modified from Andreoli 1999)...

Laboratory Test Prerenal Azotemia Acute Intrinsic Renal Failure Postrenal Obstruction... 

Postrenal ARF— Acute renal failure with an anatomical cause that is in the urinary tract. 

Nephrotoxins or ischemic disorders can initiate acute renal failure. Shock, hemorrhage, septicemia, or vasodilation due to hypertensive medication can precipitate ischemic acute renal failure. Systemic reactions to certain drugs and nephrotoxins such as aminoglycoside antibiotics and heavy metals lead to acute renal failure. The extent of retention of creatinine and urea in blood is directly related to the severity of acute renal failure. This condition is not readily reversible and, as such, should be distinguished from reversible phenomena such as prerenal or postrenal azotemia, in which there is also an increase in levels of plasma urea and creatinine (13). In volume-depleted states, for example, diarrhea, the kidney is hypoprefused. This results in increased back diffusion of urea into the circulation from the tubular fluid because of the reduced urine flow. In addition to an increase in urea levels in circulation, there is also a slow increase in creatinine levels. Plasma urea and creatinine levels can be restored to normal within 24 hours by appropriate fluid and electrolyte replacement in prerenal azotemia. In condi-... 

Renal failure can result from a variety of pathologic conditions. If renal impairment is rapid in onset and short in duration, then renal failure is described as acute. The primary cause of acute renal failure may be prerenal (i.e., acute congestive heart failure or shock), intrarenal (i.e., acute tubule necrosis) or postrenal (i.e., hypercalcemia). The condition generally is reversible however, complete restoration of renal function may take 6 to 12 months. 

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