**Question:** Investigation of choice for diagnosing intra abdominal bleeding in an unstable patient: September 2007

***Core Concept:***
The correct choice for investigating intra-abdominal bleeding in an unstable patient involves a combination of clinical examination, laboratory tests, and imaging modalities to promptly identify and treat the source of bleeding.

***Why the Correct Answer is Right:***
In unstable patients presenting with suspected intra-abdominal bleeding, the primary aim is to quickly locate and treat the bleeding source. Plain abdominal X-ray is often the first imaging modality used to evaluate for free air (gas) under the diaphragm, which indicates bowel perforation or free gas in the peritoneal cavity.

***Why Each Wrong Option is Incorrect:***
A. Ultrasound (USG) is valuable in assessing solid organ injuries and fluid collections, but it may not detect small amounts of free gas or peritoneal hemorrhage.
B. Computed tomography (CT) scan is more sensitive than plain abdominal X-ray, but using it as the first-line investigation in unstable patients is not recommended due to the increased risk of iodinated contrast-induced nephropathy and the need for sedation.
C. Abdominal paracentesis can yield a sample for microbiological analysis, but it is a highly invasive procedure with significant risk and is not a routine investigation in this scenario.
D. Endoscopy is essential for visualizing the source of gastrointestinal bleeding, but it may not be immediately accessible and may not provide a definitive diagnosis in all cases.

***Clinical Pearl:***
In unstable patients, plain abdominal X-ray serves as a rapid, readily available, and relatively safe first-line investigation to identify intra-abdominal pathology, followed by more sensitive modalities like CT scan or endoscopy based on the clinical scenario and patient condition.

***Correct Answer:***
.***Correct Answer:***
Plain abdominal X-ray (A) is the correct choice as it is readily available, relatively safe, and provides an initial assessment of the abdomen for free air (gas) under the diaphragm, which is highly suggestive of bowel perforation or free gas in the peritoneal cavity. It is a valuable initial investigation, especially in resource-limited settings, and helps guide further management.