**Question:** A 75-year old woman with chronic atrial fibrillation presented to the hospital with a 2-day history of colicky abdominal pain. The physical examination revealed hypoactive bowel sounds and diffuse abdominal tenderness. Laboratory tests showed a white cell count of 19,400 per cubic millimeter with 92% neutrophils, a blood urea nitrogen level of 42 mg per deciliter (15 mmol per liter) and a serum creatinine level of 3.0 mg per deciliter (267 micromol per liter). The most probable diagnosis in this patient would be-

A. Pneumonia
B. Acute appendicitis
C. Acute cholecystitis
D. Acute renal failure

**Correct Answer:** D. Acute renal failure

**Core Concept:**

In this scenario, we are dealing with a patient presenting with acute abdominal pain and an elevated white blood cell count along with pathognomonic laboratory findings indicative of impaired renal function. The clinical presentation is suggestive of an acute renal failure (ARF) secondary to dehydration, hypovolemia, or sepsis. The patient's history of chronic atrial fibrillation and the laboratory findings of elevated blood urea nitrogen (BUN) and creatinine levels are highly suggestive of compromised renal function.

**Why the Correct Answer is Right:**

The correct answer, acute renal failure (ARF), is derived from the patient's symptoms, signs, and laboratory results. The following points emphasize the correct diagnosis:

1. **Hypovolemia and dehydration:** The patient is 75 years old, which increases the risk of dehydration and hypovolemia due to reduced oral intake and increased fluid loss via diarrhea and vomiting. This can lead to a decrease in blood volume and impaired renal perfusion, ultimately causing renal dysfunction.
2. **Elevated white blood cell count (WBC):** An elevated WBC count, particularly with a neutrophilia (92% of neutrophils), indicates an underlying infection or inflammation. In this context, the elevated WBC count is likely a response to the renal dysfunction, as the kidneys play a significant role in regulating WBC production and release.
3. **Elevated BUN and creatinine levels:** The patient's elevated BUN and creatinine levels strongly indicate impaired renal function. BUN and creatinine levels are used as markers for assessing kidney function. An elevated level indicates reduced glomerular filtration rate (GFR) and impaired renal function.

**Why Other Answers are Incorrect:**

A. Pneumonia: While the patient does present with abdominal pain, the elevated BUN and creatinine levels, and elevated WBC count are not consistent with pneumonia. Pneumonia typically presents with respiratory symptoms and pleuritic chest pain, not abdominal pain. Additionally, pneumonia-induced renal dysfunction would not result in the elevated BUN and creatinine levels seen in this case.

B. Appendicitis: Although the patient experiences abdominal pain and elevated WBC count, the elevated BUN and creatinine levels are not consistent with appendicitis. Append