Prerenal azotemia is suggested by which pattern of BUN and creatinine?

• A. High BUN and Normal Crea
• B. High BUN and High Crea
• C. Normal BUN and High Crea
• D. Low BUN and Low Crea

Answer: (A)

Prerenal azotemia occurs when kidney perfusion falls, so the kidneys conserve water and solutes to maintain effective circulating volume. In this state, the proximal tubule reabsorbs more urea (the BUN component) while creatinine, which is filtered but not reabsorbed, does not rise unless GFR falls more markedly. The result is a BUN that increases disproportionately compared with creatinine, yielding a high BUN relative to creatinine (often a BUN:creatinine ratio > about 20:1). Early or mild prerenal changes typically show elevated BUN with a normal creatinine, which matches the described pattern. If perfusion loss is severe or prolonged, creatinine can rise as GFR declines, but the hallmark initial pattern is high BUN with normal creatinine.