**Question:** A 60-year-old woman with type 2 diabetes and end-stage renal disease receives a kidney transplant. Three weeks later, the patient presents with azotemia and oliguria. If this patient has developed acute renal failure, which of the following pathologic findings would be expected on renal biopsy?

A. Acute tubular injury
B. Chronic rejection
C. Acute tubulointerstitial nephritis
D. Glomerulonephritis

**Correct Answer:** **D. Glomerulonephritis**

**Core Concept:** Acute kidney injury (AKI), also known as acute renal failure, is a rapid decline in kidney function that can be categorized into different types. In this question, we focus on the possibility of acute tubulointerstitial nephritis (ATIN) and glomerulonephritis (GN).

**Why the Correct Answer is Right:**
Acute tubulointerstitial nephritis (ATIN) is a subtype of acute kidney injury (AKI) where inflammation occurs within the kidney's tubules and interstitium. ATIN can be caused by medications, infections, or autoimmune disorders such as vasculitis. It is important to note that ATIN does not involve glomeruli (glomerulonephritis) which is the focus of the correct answer.

**Why Each Wrong Option is Incorrect:**

**A. Acute tubular injury (ATI)**: ATI is a broader term for acute kidney injury (AKI) and does not specifically address the correct answer, which is glomerulonephritis.

**B. Chronic rejection (CR):** Chronic rejection is a condition resulting from the body's immune system attacking the transplanted kidney, not the native kidney. It is a complication of renal transplantation and does not explain the given patient's scenario.

**C. Acute tubulointerstitial nephritis (ATIN):** As mentioned earlier, ATIN is a subtype of AKI and not the correct answer for the patient with end-stage renal disease and kidney transplant, as it does not address the glomeruli involvement.

**Clinical Pearl:**
In patients with end-stage renal disease and kidney transplantation, the main concern is acute glomerulonephritis, which can occur post-transplant and lead to acute kidney injury (AKI). Glomerulonephritis affects the glomeruli, which are essential for filtering blood in the kidneys. This can lead to reduced glomerular filtration rate (GFR) and impaired urine production, resulting in azotemia and oliguria.

In summary, the correct answer (D) is glomerulonephritis, which is an acute inflammatory disease affecting the glomeruli in the kidney. Understanding the correct answer helps in formulating an appropriate treatment plan and prognosis for this patient.