From Dog

Azotemia is defined as abnormally high levels of urea, creatinine and other nitrogenous compounds detectable in blood samples.

In dogs, azotemia is usually a reflection of either acute renal injury or chronic renal disease. Circulatory disorders such as congestive heart failure may also result in azotemia due to reduced renal perfusion.

Three forms have been classified in dogs, relating to the cause of azotemia:

Prerenal azotemia decreased renal perfusion hemmorhage, shock, congestive heart failure - BUN:Cr ration > 20
Renal azotemia acute renal injury, glomerulonephritis BUN:Cr < 15
Postrenal azotemia urolithiasis, Leptospirosis, transitional cell carcinoma BUN:Cr >15