Medical Oncologist
Side effects
Low White Cells and Infection Risk — on Targeted Therapy
Many targeted therapies lower your white blood cell count. The count itself does not feel like anything — but it means your body is less able to fight off infections, and any fever during that period needs to be treated as a medical event, not an ordinary illness.
Medically reviewed by Dr. T. Raghavender Reddy, Medical Oncologist, MBBS · DM (Medical Oncology) · MD (Radiation Oncology) · Last reviewed August 2026
- Common and watched for — A drop in white cells is expected with many targeted therapies and is monitored through routine blood tests.
- No obvious symptom — You cannot feel a low white cell count. Blood tests are the only reliable way to know where yours is.
- Fever changes everything — Any fever when your count is low is a medical emergency — not something to manage at home with paracetamol.
- Most people get through it safely — Knowing what to watch for and when to act is what keeps a manageable side effect from becoming a serious one.
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Many targeted therapies lower the white blood cell count — particularly neutrophils, your body's main defence against bacterial infection. On its own, a low count is manageable with monitoring. But NCCN and ASCO treat any fever that develops during a period of low white cells as a medical emergency requiring same-day hospital assessment. Call your team or go straight to hospital at the first sign of fever — do not wait to see if it passes.
If a symptom below applies to you, do not wait for a callback. Call 1800-202-8726 or go to your nearest emergency department.
What does a low white cell count actually mean?
White blood cells — particularly a type called neutrophils — are your first defence against bacterial infections. When targeted therapy lowers their number, the window between an infection starting and it becoming serious can shorten dramatically.
This is called neutropenia. You will not feel it happening. There is no pain or sensation that tells you the count is low on a given day. That is why the blood tests your oncologist schedules are not optional — they are the primary way to know where your count is between appointments.
The aim is to catch a low count early, adjust your treatment if needed, and keep you safe. Most people move through periods of neutropenia without a serious infection when they know what to watch for and act quickly on any warning sign.
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Call the helpline. It is always better to check than to wait.
How can you reduce your infection risk at home?
- Wash your hands thoroughlyBefore eating, after touching shared surfaces, and after being in public. This is the most effective single step you can take.
- Keep your mouth cleanBrush gently twice a day and rinse with salt water or a prescribed mouthwash. The mouth is a common entry point for bacteria.
- Avoid very crowded indoor spacesMarkets, busy public transport and large gatherings carry more airborne and contact risk when your count is low.
- Cook food thoroughlyMeat, poultry and eggs should be cooked through. Avoid raw or undercooked items, unpeeled fruit and raw salads during periods of very low counts.
- Ask unwell visitors to postponeAnyone with a cough, cold, stomach bug or fever should wait until they have recovered before coming to your home.
- Keep all blood test appointmentsA blood test your team has scheduled is watching for this specifically. Missing one removes the early-warning system.
- Buy and use a thermometerIt is the most important piece of equipment for managing this side effect. If you feel hot, measure your temperature rather than guessing.
- Tell your team everything you are takingIncluding ayurvedic preparations, herbal supplements and over-the-counter medicines. Some interact with targeted therapy or can mask symptoms.
How do you know whether to monitor at home, call today, or go straight in?
| What you are noticing | Monitor at home | Call your team today | Go to hospital now |
|---|---|---|---|
| Fever | None | — | Any fever, even mild — this is always a go-now situation when your count is low |
| Chills | None | Feeling cold and shivery after being outdoors | Uncontrollable shaking or rigors you cannot stop |
| How you feel overall | Slightly more tired than usual | Noticeably unwell, unable to eat or drink normally | Sudden severe deterioration or cannot keep any fluids down |
| Signs of infection anywhere | None | Any new redness, warmth, swelling or discharge at any site | Spreading rapidly, severe pain, or at a drip or line site |
| Breathing | Normal | Noticeably shorter of breath than is usual for you | Difficulty breathing, chest pain, or gasping |
| Typically starts | Varies by drug class and individual — your oncologist will tell you the period when your count is likely to be lowest | — | — |
Questions your family is probably asking
Will treatment have to stop because of low white cells?
Possibly for a short time, but not necessarily permanently. Most targeted therapy regimens build in the possibility of a dose pause or dose reduction if the white cell count drops to a level your oncologist is concerned about. A pause is a safety measure — it is not a sign that the treatment has failed or that the cancer is progressing. Your oncologist will look at your blood results and how you are feeling before deciding whether to continue, pause or adjust the dose. Many people restart successfully at the same or a slightly lower dose once the count recovers.
Should visitors wear masks at home?
This depends on where your count currently sits, and your oncologist or nurse is the right person to ask — they know your most recent result. In general, asking unwell visitors to stay away entirely is more protective than asking well ones to wear masks. If your count is very low, your team may advise being more cautious about indoor contact broadly. Follow their specific guidance for your situation rather than applying a general rule, and ask them directly at your next appointment or blood test review.
Is it safe to visit a temple or place of worship?
This is a reasonable question and your faith practices matter. The concern is not the place itself but crowding and contact with shared surfaces. If the space is very crowded, if you are asked to touch surfaces or objects handled by many others, and if your count is currently low, there is a real infection risk. Some people attend at quieter times, avoid touching shared surfaces, and wash their hands immediately afterwards. Tell your oncologist you want to continue attending and ask what precautions make sense for your specific count — they will give you a practical answer rather than a blanket refusal.
What if I cannot reach my team and I feel unwell?
Go to the nearest emergency department and tell them clearly that you are on targeted therapy and may have a low white cell count. Those words change how quickly you are seen. If you have a recent blood test result showing your count was low, bring it or photograph it on a phone. Emergency staff are trained for neutropenic fever and will contact your oncology team from there. Do not wait for a callback if you have any fever, cannot keep fluids down, or feel suddenly worse. The risk of delay is too high to justify it.
Can I have a vaccination while my count is low?
Ask your oncologist before having any vaccination during treatment. Live vaccines — including some travel vaccines — are generally avoided during immunosuppression because the live virus can cause the infection it is meant to prevent. Inactivated vaccines are usually safer but may not produce as strong an immune response when white cells are low. Influenza vaccination is often recommended, but the timing relative to your treatment cycle matters. Do not assume either way — raise it at your next appointment so the decision can be made with your current count in mind.
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Common questions
Frequently asked questions
How will I know if my white cell count is low?
You will not feel it directly — a low white cell count has no obvious symptom of its own. Your oncologist finds it through the blood tests scheduled around your treatment. That is why those appointments are important: they are the primary way to catch a low count before an infection develops. Between tests, the signal to watch for is not the count itself but any symptom that could mean an infection has started — particularly any fever, chills, or sudden change in how you feel.
Which targeted therapies commonly cause a low white cell count?
Several classes of targeted therapy cause neutropenia as a recognised side effect, including CDK4/6 inhibitors used in breast cancer and BCR-ABL inhibitors used in certain leukaemias, among others. The likelihood and timing varies by drug. Your oncologist should have discussed this when treatment started. If the information was not clear, asking specifically which side effects your drug is associated with and what blood monitoring is planned around them is a reasonable question at your next appointment.
Can I eat normally, including at restaurants?
Your team will advise based on your current count. During periods when your count is very low, food hygiene matters more than usual. Freshly cooked food at high temperature is safer than items that have been sitting out, handled by many people, or are raw. Avoiding unpeeled fruit, raw salads, chutneys from shared pots and undercooked meat or eggs is a reasonable general approach. Ask your oncologist or nurse whether a specific neutropenic diet has been recommended for you — guidance varies depending on how low your count actually is.
What should I say when I arrive at the emergency department?
Say clearly: 'I am on targeted therapy for cancer and I may have a low white cell count.' Those words are understood by emergency triage staff and change how quickly you are assessed. Neutropenic fever is a recognised medical emergency and most emergency departments have a pathway for it. If you have your treatment summary card, drug name or a recent blood test result, bring it or have a family member photograph it. If you are too unwell to speak, make sure the person with you knows what to say.
How long does neutropenia from targeted therapy usually last?
It varies considerably by drug class and individual. Some targeted therapies cause a predictable dip that recovers before the next dose. Others cause a more sustained reduction that is monitored throughout treatment. NCCN and ASCO guidance covers monitoring schedules for specific drug classes. Your oncologist will tell you the expected pattern for your particular treatment and what blood test frequency is planned. If you have not been told when your count is likely to be at its lowest point in your cycle, that is worth asking directly so you know when to be most careful.