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Azotemia Azotemia: Blood Urea Nitrogen/Creatinine Mismatch 1201.e3

Azotemia
VetBooks.ir Differentiation and Anticipated Metabolic Changes

Parameter Prerenal Primary Renal Postrenal
Creatinine Increased Increased Increased
Blood urea nitrogen (BUN) Increased Increased Increased
Urine specific gravity Increased Decreased* Variable
Urine sediment Normal Often abnormal (e.g., casts) Often abnormal (e.g., crystals)
Urine production Decreased Variable Decreased†
Hematocrit Increased Variable, often decreased Increased
Serum potassium Normal or low Variable, increased if oliguria/anuria Increased
Serum phosphorus Normal Variable, often increased Increased
Metabolic acidosis Mild Mild to severe Mild to severe
Common causes Dehydration, hypovolemia, heart failure Chronic kidney disease, nephrotoxins, infectious Urethral obstruction, ruptured bladder
disease, glomerulonephritis
*Urine specific gravity may not be isosthenuric in cases of acute kidney injury causing oliguria or anuria.
†Until intervention removes obstruction; then increased during postobstructive diuresis.
Modified from Slatter D: Textbook of small animal surgery, St. Louis, 2003, Elsevier.
Differentials, Lists, and Mnemonics

Azotemia: Blood Urea Nitrogen/
Creatinine Mismatch

Increased BUN Plus Normal Serum Creatinine
Increased BUN
Early prerenal azotemia (decreased urine flow rate)
High-protein diet
GI hemorrhage
Tetracycline or corticosteroid administration
Fever
Loop diuretic administration (e.g., furosemide)
Severe tissue trauma
Decreased Creatinine
Decreased muscle mass (severe cachexia needed to cause significant
changes)
Increased Serum Creatinine Plus Normal to Low BUN
Decreased BUN
Hepatic insufficiency
Severe PU/PD
Low-protein diet
Increased Creatinine
Myositis/muscle trauma (unlikely)
Cooked meat diet (mild, transient changes)
Ketonemia (falsely increased)
Artifact (noncreatinine chromogens such as vitamin C, cephalosporins)
BUN, Blood urea nitrogen; GI, gastrointestinal; PU/PD, polyuria and polydipsia.
Modified from Willard M, Tvedten H: Small animal clinical diagnosis by laboratory methods, ed 5,
St. Louis, 2012, Saunders.

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