**Core Concept:** Portal hypertension is a condition characterized by increased pressure within the portal venous system. It can present with bleeding from esophageal varices, which are dilated veins in the esophagus caused by backflow of blood from the larger veins into the smaller ones. In this scenario, the cause of the portal vein occlusion leads to portal hypertension, without liver cirrhosis as a contributing factor.

**Why the Correct Answer is Right:** The correct answer is D, "Anticoagulation screen." Anticoagulation screen evaluates the patient's coagulation status to identify any thrombosis or clotting disorder. In this case, the occlusion of the portal vein is the cause of the increased portal pressure. Anticoagulation screen can help identify any underlying clotting disorder that might be contributing to the portal vein occlusion, thus revealing the predisposing factor for the patient's condition.

**Why Each Wrong Option is Incorrect:**

A. Portal venography: This test would visualize the portal venous system and the occlusion; however, it does not address the cause of the occlusion or the predisposing factor for the patient's condition.

B. Liver function tests (LFTs): LFTs assess liver function and do not directly determine the cause of the portal vein occlusion or identify the predisposing factor for the patient's esophageal variceal bleeding.

C. Ultrasound scan: Ultrasound scan is useful for assessing liver morphology and function, but it does not specifically identify the cause of portal vein occlusion or determine the predisposing factor for the patient's condition.

**Clinical Pearl:** In cases of portal vein occlusion without liver cirrhosis, identifying the cause is crucial to establish appropriate management and prevent further complications. This is particularly important in patients with portal hypertension, such as those with esophageal variceal bleeding, to prevent rebleeding and related complications.