Which laboratory change is most suggestive of renal allograft rejection?

• A. Decreasing creatinine level
• B. Rising creatinine with decreased urine output
• C. Dehydration with low urine volume
• D. High potassium with normal creatinine

Answer: (C)

When a renal allograft is rejected, the transplanted kidney’s ability to filter blood declines, so the glomerular filtration rate drops. That means waste products build up in the blood, with creatinine rising, and the kidney produces less urine, leading to oliguria. So the combination of a rising serum creatinine with decreased urine output is the most telling sign of graft rejection. Other patterns can occur for different reasons—decreasing creatinine suggests improving function, dehydration can lower urine output without indicating rejection, and a high potassium level with a normal creatinine points to other issues—so they’re not as specific to rejection. In clinical practice, rising creatinine over time in a transplant patient triggers evaluation for rejection and possible changes in immunosuppressive therapy, sometimes with a biopsy to confirm.