Febrile neutropenia in adults

Neutrophils are made in the bone marrow and released into the bloodstream. They are one part of the immune system and help the body respond to infection.

The absolute neutrophil count, or ANC, measures neutrophils in the blood. A total white-cell count is a different measure and cannot be used in place of the ANC.

When neutrophil levels are very low, infection risk can rise. The body's response may also be less obvious. Redness, swelling, pus, pain or fever may be mild or absent even when an infection is serious.

Risk is not decided by the ANC alone. It also depends on the cause, how low the count is expected to fall, how long it may stay low, the underlying illness, treatment, other health conditions and how unwell the person is now. These factors need clinical assessment and should not be used as a home risk calculator.

Neutropenia itself often causes no symptoms. A blood test is needed to measure the ANC.

Fever may be the first or only sign of infection. Other possible signs include chills or shivering, a sore throat, cough or breathing change, mouth ulcers, diarrhoea, pain when passing urine, or new redness, swelling, pain or discharge around the skin, a wound or an intravenous line.

Some serious infections do not cause fever. Feeling suddenly or seriously unwell matters, especially after recent anticancer treatment or when a care plan says there is a high risk of severe neutropenia.

Febrile neutropenia does not automatically mean sepsis. Neutropenic sepsis is a related but different diagnosis in which infection causes life-threatening organ problems in a person with neutropenia.

Urgent tests answer several different questions.

How unwell are you now?

The clinical team will check your temperature, breathing, heart rate, blood pressure, alertness and other signs. They will examine you for possible sources of infection.

Are neutrophils low, and are organs being affected?

A full blood count measures the ANC and other blood cells. Other blood tests can check kidney and liver function and look for signs that the body is under stress.

Could an infection be present, and where might it be?

Blood cultures are usually collected. Urine, respiratory or other samples, and imaging may be used when symptoms or the examination suggest a source.

Tests should not delay time-critical treatment when febrile neutropenia or serious infection is suspected. If you are at recognised high risk, do not wait for a current ANC before seeking help.

Before an emergency

• Know the fever threshold and emergency service in your treatment plan.
• Keep a working digital thermometer and use the measurement method taught by your treating service.
• Keep your treatment details and emergency contact instructions easy to find.
• Ask the treating team or pharmacist how to use fever-reducing medicines safely. These medicines can hide infection signs.

When fever or serious illness starts

Follow the urgent action above. If it can be done without delaying care, record your temperature before taking a fever-reducing medicine. Do not use a lower temperature after medicine as a reason to stay home.

A named oncology or haematology emergency service can replace the emergency department only when it is part of your care plan, immediately available and able to assess you urgently. Trying to contact a service must not delay travel or emergency assessment.

During urgent assessment

The clinical team will assess how unwell you are, collect the tests that matter and start prompt treatment when infection is suspected. Treatment is often started before the source or exact organism is known.

Some people may later receive care through a formal outpatient pathway. This decision is made by the treating team after clinical risk assessment. The need for admission or discharge cannot be decided safely at home.

Febrile neutropenia can worsen quickly, but the course varies. It depends on the cause and duration of neutropenia, the infection, other health conditions, current stability and how soon effective treatment begins.

Early assessment gives the clinical team time to find serious problems and start time-critical treatment. It does not mean that infection, sepsis or hospital admission is certain.

Neutrophil counts can change over time. Ask the treating clinician whether future treatment or the underlying condition changes your risk plan.

Fever can come from infection or a non-infectious cause. Symptoms may also be affected by the underlying illness, medicines or treatment. Because these causes cannot be separated safely at home, an at-risk person should still follow the urgent pathway.

Not every adult with a low ANC has the same risk. If neutropenia is mild, stable or found by chance and no high-risk plan applies, ask the clinician who ordered the blood test what fever or illness should prompt emergency care.

• Waiting for another temperature reading after 38.0°C can delay urgent assessment.
• Waiting for a routine appointment, the next day or a current ANC result is not safe when a high-risk person has reached the applicable threshold or feels seriously unwell.
• Using fever-reducing medicine to test whether the illness is serious is unreliable. A lower reading after medicine does not remove the need for assessment.
• Choosing home or outpatient care without clinical assessment is not recommended. Any outpatient pathway requires assessment and an established service.

• Neutrophil: A type of white blood cell that helps the body respond to infection.
• Absolute neutrophil count (ANC): A blood-test measure of the number of neutrophils in the blood.
• Neutropenia: A lower-than-normal number of circulating neutrophils.
• Febrile neutropenia: Fever with confirmed or expected severe neutropenia.
• Neutropenic sepsis: Life-threatening organ problems caused by infection in a person with neutropenia. It is not another name for every episode of febrile neutropenia.