Hemorrhagic ascites due to trauma or surgical complication: This is the most likely diagnosis because dark red ascitic fluid is often indicative of blood in the peritoneal cavity, which can occur due to trauma, surgical complications, or other conditions that lead to bleeding into the abdominal space.

Malignancy-related hemorrhagic ascites: Certain cancers, especially those originating in the abdomen such as ovarian, gastrointestinal, or liver cancers, can cause hemorrhagic ascites due to tumor rupture or invasion into blood vessels.
Tuberculous peritonitis with hemorrhage: Although less common, tuberculosis can cause peritonitis and, in rare instances, lead to hemorrhage into the ascitic fluid.
Pancreatic disease (e.g., pseudocyst rupture): Conditions like pancreatitis or the rupture of a pancreatic pseudocyst can lead to hemorrhagic ascites.

Ruptured ectopic pregnancy: Although less likely, a ruptured ectopic pregnancy can cause sudden, severe abdominal pain and hemorrhagic ascites. Missing this diagnosis can be fatal.
Ruptured abdominal aortic aneurysm: This is a medical emergency that can present with abdominal pain and hemorrhagic ascites. Prompt diagnosis is crucial for survival.
Intra-abdominal vascular rupture (e.g., hepatic or splenic artery aneurysm): These conditions are rare but can cause sudden, severe bleeding into the peritoneal cavity.

Chylous ascites with hemorrhage: Chylous ascites is the accumulation of lymphatic fluid in the peritoneal cavity, which can rarely become hemorrhagic.
Hemorrhagic ascites due to coagulopathy: Conditions that affect blood clotting can lead to spontaneous bleeding into the peritoneal cavity, although this is less common.
Intrauterine death with subsequent hemorrhagic ascites: In rare cases, the death of a fetus can lead to maternal coagulopathy and hemorrhagic ascites, although this would be accompanied by other symptoms related to the pregnancy.