Bacterial infection: This is the most common cause of post-biopsy fever, often due to introduction of bacteria into the biopsy site during the procedure. The risk is higher with certain types of biopsies, such as liver or kidney biopsies, where the risk of bleeding and subsequent infection is increased.

Reaction to the biopsy procedure: Some patients may experience a febrile reaction to the biopsy itself, which could be due to the trauma caused by the needle or the introduction of foreign material into the body.
Hematoma or abscess formation: Depending on the location and type of biopsy, there is a risk of hematoma or abscess formation, both of which can cause fever.
Allergic reaction: Though less common, an allergic reaction to materials used in the biopsy (e.g., latex, medications) could potentially cause fever.

Sepsis: Although less likely, sepsis is a potentially life-threatening condition that can arise from an infection at the biopsy site. Early recognition and treatment are crucial.
Endocarditis: In patients with pre-existing heart conditions, there is a small risk of developing endocarditis following a biopsy, particularly if the biopsy involves a site with a high risk of bacteremia.
Pneumonia or other systemic infections: Depending on the type of biopsy and the patient's overall health, there is a risk of developing pneumonia or other systemic infections that could present with fever.

Fungal infections: Fungal infections are rare but can occur, especially in immunocompromised patients.
Vasovagal reaction with secondary infection: A vasovagal reaction during the biopsy could potentially lead to complications, including infection, though this is rare.
Foreign body reaction: A reaction to a foreign body, such as a retained biopsy needle fragment, could theoretically cause fever, though this is exceedingly rare with modern biopsy techniques.