Differential Diagnosis for Decreasing Hematocrit after Fever and Tachycardia

Single Most Likely Diagnosis

• Hemorrhage: This is the most straightforward cause of a decreasing hematocrit, especially when accompanied by symptoms like fever and tachycardia, which could indicate an infectious or inflammatory process leading to bleeding.

Other Likely Diagnoses

• Sepsis: Fever and tachycardia are common presentations of sepsis, which can lead to a decrease in hematocrit due to various mechanisms including hemodilution from fluid resuscitation, microangiopathic hemolytic anemia, or disseminated intravascular coagulation (DIC).
• Hemolytic Anemia: Conditions like autoimmune hemolytic anemia or drug-induced hemolysis could present with fever, tachycardia, and a drop in hematocrit due to increased red blood cell destruction.
• Severe Infection: Certain infections, such as malaria or babesiosis, can directly cause hemolysis leading to a decrease in hematocrit.

Do Not Miss Diagnoses

• Ruptured Aortic Aneurysm or Other Major Vascular Injury: Although less common, these conditions can present with sudden onset of symptoms including fever (due to inflammation), tachycardia, and a significant drop in hematocrit due to internal bleeding.
• DIC (Disseminated Intravascular Coagulation): This condition can lead to both clotting and bleeding and is often associated with severe infections, trauma, or malignancies. It can cause a decrease in hematocrit due to consumption of platelets and clotting factors.
• Severe Trauma: Internal bleeding from trauma can lead to a decrease in hematocrit, and associated fever and tachycardia could be due to the stress response or infection.

Rare Diagnoses

• Thrombotic Thrombocytopenic Purpura (TTP): A rare blood disorder characterized by the formation of blood clots in small blood vessels throughout the body, which can lead to a decrease in hematocrit among other symptoms.
• Paroxysmal Nocturnal Hemoglobinuria (PNH): A rare, acquired, life-threatening disease of the blood characterized by the destruction of red blood cells (hemolysis), bone marrow failure, and the potential for blood clot formation.
• Hemophagocytic Lymphohistiocytosis (HLH): A rare disorder of the immune system where it produces too many activated immune cells called macrophages and lymphocytes, which can lead to a decrease in hematocrit due to hemophagocytosis.