Final answer:
An elevated blood urea nitrogen (BUN) level is most indicative of prerenal azotemia in a patient with decreased urine output and heart failure. This suggests decreased kidney perfusion without damage to the kidney tissue itself.
Step-by-step explanation:
The nurse caring for a patient with heart failure notes the patient has decreased urine output of
. When considering laboratory findings that aid in the diagnosis of prerenal azotemia in this patient, an elevated blood urea nitrogen (BUN) level is most indicative. Prerenal azotemia refers to the condition where there is a decreased perfusion leading to hypofiltration in the kidneys, resulting in the accumulation of nitrogenous waste products like BUN in the blood. Factors such as medication interfering with normal bladder emptying, benign prostatic hypertrophy, prostate cancer, kidney stones, abdominal malignancies, and obstructed urinary catheter could all potentially lead to prerenal azotemia. In the case of prerenal azotemia, the renal tissue itself is not damaged, which typically results in a preserved creatinine level within the normal range.
The diagnosis of renal failure often includes measuring serum creatinine levels along with BUN. While a significant rise in creatinine can indicate intrinsic kidney damage (renal causes of azotemia), a high BUN level with a relatively normal creatinine level suggests a prerenal cause. Therefore, the correct answer to the question is A. Elevated blood urea nitrogen (BUN).