Fever During Chemotherapy: What to Do and When It’s an Emergency

A temperature of 38.0 °C or higher during chemotherapy is a reason to call your doctor straight away, at any time of day or night — not to wait until morning. Chemotherapy can lower the number of neutrophils (the blood cells that fight bacteria), and when that happens an infection can develop very quickly, with a raised temperature sometimes its only sign. This condition is called febrile neutropenia, and it is treated as an emergency.

A temperature of 38.0 °C or higher during chemotherapy: don’t wait and don’t bring it down yourself — call your oncologist or your clinic’s out-of-hours line. If you can’t get through, or you have any of the red flags listed below, call your local emergency number (911 in the US, 999 in the UK, 112 in the EU).

What febrile neutropenia is

Febrile neutropenia is a combination of two things: a raised temperature and a low neutrophil count.

At home you don’t know your neutrophil count. So the guide for patients is simpler: the CDC (US Centers for Disease Control and Prevention) advises calling your doctor immediately if your temperature is 38.0 °C or higher, and calls a fever during chemotherapy an emergency. Whether it is neutropenia or not will be decided by your doctor based on a blood test.

The American Cancer Society adds: ask your care team what temperature they consider the threshold in your case. If they give you a different number, go by that.

Why it’s an emergency

Neutrophils are the first line of defence against bacteria. When there are too few of them, the body can neither contain an infection nor react to it properly: there may be no redness, pus or cough, and a raised temperature remains the only signal. The American Cancer Society states plainly that with neutropenia an infection can very quickly become life-threatening.

That’s why, with febrile neutropenia, doctors don’t wait for culture results. Under ASCO/IDSA guidelines, the first dose of a broad-spectrum antibiotic is given within an hour of presentation and initial assessment. The Russian Society of Clinical Oncology (RUSSCO) puts it this way: antibiotic treatment is started as early as possible, usually right after blood is taken for culture. Every hour you wait at home pushes that clock back.

What to do if your temperature rises

1. Take your temperature again if you doubt the first reading — but don’t drag this out for hours.
2. Call your oncologist or the out-of-hours line of the clinic where you are being treated. Tell them: what your temperature is, when your last chemotherapy was, which drugs you received, and whether you have chills or other symptoms.
3. If you can’t get through or you feel unwell, call your local emergency number (911 in the US, 999 in the UK, 112 in the EU) and tell them straight away that you are having chemotherapy.
4. Don’t take fever reducers before you call, unless your doctor has given you different instructions in advance. The American Cancer Society advises checking with your care team first: they may ask you not to take anything. A tablet will lower the temperature but won’t stop the infection, and it will make it harder for the doctor to assess the situation.
5. Take with you the summary from your last cycle, a list of your medicines and your latest blood test results.

I usually suggest writing down the out-of-hours number and a short “what to do if I have a temperature” plan on a note on the fridge. When you’re shivering and frightened, it’s easier to follow a ready-made list.

Red flags: when to call without waiting for a temperature

Contact your doctor even if your temperature is below 38 °C if you have signs of infection listed by the American Cancer Society:

• chills or sweating;
• cold, clammy or pale skin;
• cough or difficulty breathing;
• new or worsening confusion;
• pain when passing urine;
• little or no urine, or dark orange or brown urine.

Call your local emergency number straight away (911 in the US, 999 in the UK, 112 in the EU) if you have difficulty breathing, confusion, severe weakness or dizziness, or little or no urine — especially together with a temperature.

What happens when you seek help

Patients often ask me whether they’re “raising the alarm for nothing”. They aren’t. Here is what usually happens next, according to RUSSCO and ASCO/IDSA guidelines.

Tests. You’ll be examined, and blood will be taken for a full blood count with differential (to find out your neutrophil level), biochemistry and blood cultures — to identify the cause of the infection. If you have a port or a central line, blood cultures are also taken from it. Other tests are ordered depending on your symptoms.

Antibiotics. They are started right after blood is taken for culture, without waiting for the results: cultures take several days, and with neutropenia you can’t wait that long. The first dose is given intravenously.

Risk assessment. The doctor assesses how severe the infection might be. For this the MASCC score is used: a score of 21 or higher means low risk, below 21 means high risk. The score takes into account how severe the symptoms are, blood pressure, age, dehydration, certain other conditions, and where the fever started — at home or in hospital.

Where you’re treated. High-risk patients are treated in hospital. Under ASCO/IDSA guidelines, some low-risk patients can be treated as outpatients — but only after examination, the first dose of antibiotics and observation in the clinic for at least 4 hours. RUSSCO adds conditions: there are family or friends nearby to help, there is quick access to a doctor and a way to get to the clinic fast. This decision is made by the doctor, not by the patient over the phone.

If it turns out that your neutrophils are normal and the temperature has a different cause, that’s a good outcome — not a “false alarm”.

When the risk is highest: the nadir

The white cell count doesn’t drop immediately after chemotherapy. According to the CDC, it is usually lowest between day 7 and day 12 after treatment and can stay low for up to a week. This period is called the nadir.

That doesn’t mean a temperature doesn’t matter on other days. The exact timing depends on the regimen, so ask your doctor when your nadir is expected. I explain how to read your results before a cycle in my article on blood tests before chemotherapy.

Can it be prevented?

Preventive medication. For regimens with a high risk of febrile neutropenia (more than 20%, according to RUSSCO), primary prevention with colony-stimulating factors (G-CSF) is recommended — drugs that stimulate the production of neutrophils. At a risk of 10–20%, the doctor weighs additional factors that increase it — for example, age over 65 or repeated courses of treatment. If you’ve been prescribed these injections, don’t skip them.

Everyday measures. The CDC advises:

• wash your hands often — and so should everyone who is in contact with you, including family and medical staff; don’t be shy about asking them;
• take your temperature whenever you feel hot, have chills, a flushed face or just feel unwell.

It helps to know in advance what happens at each stage of a cycle: then it’s easier to work out which day of the cycle you’re on and how likely the nadir is.

Thermometer at home: what matters

• Use an oral thermometer (measuring in the mouth): the thresholds in the guidelines are given for this method. If you’re used to measuring under the arm, ask your doctor what number to go by.
• Don’t take your temperature rectally if you might have neutropenia: the American Cancer Society specifically warns against this.
• Write down the time and value of each reading: this will help your doctor.

Questions to ask your oncologist

• What temperature is my cue to call?
• Which number do I call at night and at weekends?
• When is the nadir expected with my regimen?
• What is my regimen’s risk of febrile neutropenia, and do I need G-CSF prevention?
• Can I take fever reducers, and in which situations?

If you’re already on treatment and want to put together a clear plan in advance for a temperature and other side effects, I can help you work through it in a consultation during treatment.

Sources

1. Практические рекомендации по диагностике и лечению фебрильной нейтропении (Practice guidelines for the diagnosis and treatment of febrile neutropenia) — Russian Society of Clinical Oncology (RUSSCO), 2023 (revised 2024)
2. Outpatient Management of Fever and Neutropenia in Adults Treated for Malignancy — ASCO/IDSA, Journal of Clinical Oncology, 2018
3. Fever — American Cancer Society
4. Preventing Infections in Cancer Patients — CDC