What causes febrile neutropenia?

Neutrophils are white blood cells that help control bacteria and fungi. Chemotherapy can temporarily slow the bone marrow, so fewer neutrophils enter the bloodstream. The lowest point may occur after a treatment session and before the marrow recovers.

When neutrophils are low, an infection may progress without obvious local signs. A fever may be the first or only warning. The cause can be an infection from the skin, mouth, lungs, gut, urinary system or a treatment device; sometimes no source is found immediately.

Before treatment, ask your oncology team for the exact temperature threshold and telephone number to use day or night. Check your temperature with a reliable thermometer if you feel hot, chilled, unusually tired or unwell. Do not take fever-reducing medicine to hide a fever unless your team tells you to.

Follow instructions about hand hygiene, food safety, mouth care and avoiding contact with people who are ill. Your team may review blood counts, examine you and arrange tests to look for infection. Antibiotics or other treatment may be needed quickly. Learn more about [Chemotherapy](/treatments/systemic-therapy/chemotherapy/).

Treat a fever during a period of low neutrophils as an urgent problem. Contact your oncology team immediately using the emergency instructions they provided, even if you otherwise feel well. Go to urgent care or an emergency department if you cannot reach the team, or if you have shaking chills, confusion, breathing difficulty, severe weakness or dizziness.

When might my neutrophil count be lowest? What temperature should trigger an immediate call? Should I keep a thermometer at home? Which medicines should I avoid before speaking with you? What should I do if I have a central line or other treatment device?