Febrile Neutropenia Disease Background

Last updated: 07 November 2025
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Introduction

Content on this page:

Introduction

Introduction

Febrile neutropenia is defined as a single oral temperature of ≥38.3°C (101°F) or two consecutive readings of ≥38.0°C (100.4°F) over 2 hours and an absolute neutrophil count (ANC) of <500/μL (<0.5 x 109/L) or an ANC of <1,000/μL that is expected to decline to ≤500/μL (<0.5 x 109/L) over the next 48 hours. Severe neutropenia is defined as ANC <500/μL (<0.5 x 109/L), while profound neutropenia is defined as ANC <100/μL (<0.1 x 109/L).

The risk of febrile neutropenia is directly proportional to the duration and severity of neutropenia.

Epidemiology

Febrile neutropenia is common among patients receiving cytotoxic chemotherapy. It is estimated that 10-50% of patients with solid tumors and 80% with hematologic malignancies will develop fever during chemotherapy-induced neutropenia. The mortality rates in patients suffering from solid tumors and hematologic malignancies are 5% and 11%, respectively.

In studies in Singapore, the mortality rate attributed to post chemotherapy febrile neutropenia is between 3 and 8% and is similar to results from American and European studies.

Etiology

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The source of infection is identified in 20-30% of febrile neutropenia episodes. Bacteria are the most common cause of infection. Fungal infections are common in high-risk patients with febrile neutropenia. Viral infections (eg herpes, varicella-zoster, respiratory viruses) may also cause febrile neutropenia. 

Pathophysiology

The factors contributing to febrile neutropenia include a direct effect of chemotherapy or immunosuppressive therapy on the immune system and on mucosal barriers and immunodeficiencies associated with primary malignancy. Chemotherapy destroys carcinogenic cells but also attacks some normal cells, including essential elements of the immune system. Neutrophils, which are the first line of the body’s defense, commonly decrease during cancer treatment. The fever is related to the production of cytokines, which are mediated by exogenous pyrogens.