**Question:** Forty eight hours after sustaining a blunt abdominal injury, a 15 year old boy presents with hematuria and pain in the left side of abdomen. On examination, he has a pulse rate of 96/minute with a BP of 110/70 mmHg. His Hb is 10-8 gm% with a PCV of 31%. Abdominal examination revealed tenderness in left lumbar region but no palpable mass. The most appropriate investigation to diagnose and find the extent of renal injury would be-

A. Abdominal ultrasound
B. Serum creatinine levels
C. Computed tomography angiography (CTA)
D. Renal scintigraphy

**Correct Answer:** C. Computed tomography angiography (CTA)

**Core Concepts:**

The patient is a 15-year-old boy with a history of blunt abdominal trauma, presenting with hematuria, left abdominal pain, and hemodynamic instability (tachycardia, hypotension, decreased hemoglobin, and increased PCV). These symptoms and signs suggest significant blood loss and potential organ injury.

**Why the Correct Answer is Right:**

Computed tomography angiography (CTA) is the most appropriate investigation to diagnose and assess the extent of renal injury in this scenario. It provides detailed visualization of the renal vasculature, parenchyma, and surrounding structures.

**Why Other Options are Incorrect:**

A. Abdominal ultrasound: Although ultrasound can detect free fluid, hemoperitoneum, and renal contusions, it is less sensitive for detecting arterial injuries and has limited spatial resolution compared to CTA.

B. Serum creatinine levels: Serum creatinine levels are a marker of kidney function but do not provide information regarding the presence or severity of renal injuries. Assessing renal function is essential, but it is not the primary investigation needed to diagnose renal injury.

D. Renal scintigraphy: Renal scintigraphy is used to assess renal function but lacks anatomical detail and is not specific for detecting renal injuries.

**Clinical Pearls:**

1. In cases of blunt abdominal trauma, CTA is crucial for assessing renal injury, as it provides detailed anatomical information and detects arterial injuries.
2. Serum creatinine levels are important for assessing kidney function but are not a standalone diagnostic tool for renal injury.
3. Abdominal ultrasound is useful for detecting free fluid, hemoperitoneum, and renal contusions but is less sensitive for arterial injuries compared to CTA.
4. Renal scintigraphy is useful for assessing renal function but lacks anatomical detail and is not specific for detecting renal injuries.