The increased nephron tubular pressure (due to fluid back-up) causes increased reabsorption of urea, elevating it abnormally relative to creatinine. Persistent obstruction damages the tubular epithelium over time, and renal azotemia will result with a decreased BUN:Cr ratio. Signs and symptoms
Oliguria or anuria (decreased or absent urine output)
Fatigue
Asterixis (flapping tremor)
Decreased alertness
Confusion
Pale skin
Tachycardia (rapid pulse)
Xerostomia (dry mouth)
Thirst
Edema, anasarca (swelling)
Orthostatic blood pressure (fluctuates depending on body position)
Uremic frost, a condition that occurs when urea and urea derivatives are secreted through the skin in sweat, which evaporates away to leave solid uric compounds, resembling a frost.A urinalysis will typically show a decreased urine sodium level, a high urine creatinine-to-serum creatinine ratio, a high urine urea-to-serum urea ratio, and concentrated urine (determined by osmolality and specific gravity). None of these is particularly useful in diagnosis.In pre-renal and post-renal azotemias, elevation of urea exceeds that of the creatinine (i.e., BUN>12*creatinine). This is because urea is readily reabsorbed by the kidneys while creatinine is not. In congestive heart failure (a cause of pre-renal azotemia) or any other condition that causes poor perfusion of kidneys, the sluggish flow of glomerular filtrate results in excessive absorption of urea and elevation of its value in blood. Creatinine, however, is not absorbable and therefore does not rise significantly. Stasis of urine in post-renal azotemia has the same effect. Treatment
Prompt treatment of some causes of azotemia can result in restoration of kidney function; delayed treatment may result in permanent loss of renal function.
This generally leads to a BUN:Cr ratio > 20 and a fractional excretion of Na of < 1% and an elevated urine osmolarity. Primary renal azotemia
Renal azotemia (acute kidney failure) typically leads to uremia. It is an intrinsic disease of the kidney, generally the result of kidney parenchymal damage. Causes include kidney failure, glomerulonephritis, acute tubular necrosis, or other kidney disease.The BUN:Cr in renal azotemia is less than 15. In cases of kidney disease, glomerular filtration rate decreases, so nothing gets filtered as well as it normally would. However, in addition to not being normally filtered, what urea does get filtered is not reabsorbed by the proximal tubule as it normally would be. This results in lower levels of urea in the blood and higher levels of urea in the urine as compared to creatinine. Creatinine filtration decreases, leading to a higher amount of creatinine in the blood. Third spacing of fluids such as peritonitis, osmotic diuresis, or low aldosterone states such as Addisons disease all elevate urea. Postrenal azotemia
Blockage of urine flow in an area below the kidneys results in postrenal azotemia. It can be caused by congenital abnormalities such as vesicoureteral reflux, blockage of the ureters by kidney stones, pregnancy, compression of the ureters by cancer, prostatic hyperplasia, or blockage of the urethra by kidney or bladder stones. Like in prerenal azotemia, there is no inherent renal disease. The increased resistance to urine flow can cause back up into the kidneys, leading to hydronephrosis.The BUN:Cr in postrenal azotemia is initially >15.